SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 ________________ Schedule 13G ________________ INFORMATION TO BE INCLUDED IN STATEMENTS PURSUANT TO RULES 13d-1(b),(c) AND (d) AND AMENDMENTS THERETO FILED PURSUANT TO 13d-2 UNDER THE SECURITIES EXCHANGE ACT OF 1934* Pioneer Natural Resources Company (Name of Issuer) Common Stock (Title of Class of Securities) 723787107 (CUSIP Number) October 20, 2015 (Date of Event Which Requires Filing of this Statement) Check the appropriate box to designate the rule pursuant to which this Schedule is filed: [ ] Rule 13d-1(b) [X] Rule 13d-1(c) [ ] Rule 13d-1(d) ___________ * The remainder of this cover page shall be filled out for a reporting person's initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter the disclosures provided in a prior cover page. The information required in the remainder of this cover page shall not be deemed to be "filed" for the purpose of Section 18 of the Securities Exchange Act of 1934 ("Act") or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes). Schedule 13G PAGE 2 of 20 CUSIP No. 723787107 _____________________________________________________________________________ (1) NAME OF REPORTING PERSON S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON Viking Global Investors LP _____________________________________________________________________________ (2) CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (a) [ ] (b) [x] _____________________________________________________________________________ (3) SEC USE ONLY _____________________________________________________________________________ (4) CITIZENSHIP OR PLACE OF ORGANIZATION Delaware _____________________________________________________________________________ NUMBER OF (5) SOLE VOTING POWER 0 SHARES ______________________________________________________________ BENEFICIALLY (6) SHARED VOTING POWER 8,962,186 OWNED BY ______________________________________________________________ EACH (7) SOLE DISPOSITIVE POWER 0 REPORTING ______________________________________________________________ PERSON WITH (8) SHARED DISPOSITIVE POWER 8,962,186 _____________________________________________________________________________ (9) AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 8,962,186 _____________________________________________________________________________ (10) CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES [ ] _____________________________________________________________________________ (11) PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9) 6.0% _____________________________________________________________________________ (12) TYPE OF REPORTING PERSON PN _____________________________________________________________________________ Schedule 13G PAGE 3 of 20 CUSIP No. 723787107 _____________________________________________________________________________ (1) NAME OF REPORTING PERSON S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON Viking Global Performance LLC _____________________________________________________________________________ (2) CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (a) [ ] (b) [x] _____________________________________________________________________________ (3) SEC USE ONLY _____________________________________________________________________________ (4) CITIZENSHIP OR PLACE OF ORGANIZATION Delaware _____________________________________________________________________________ NUMBER OF (5) SOLE VOTING POWER 0 SHARES ______________________________________________________________ BENEFICIALLY (6) SHARED VOTING POWER 5,952,772 OWNED BY ______________________________________________________________ EACH (7) SOLE DISPOSITIVE POWER 0 REPORTING ______________________________________________________________ PERSON WITH (8) SHARED DISPOSITIVE POWER 5,952,772 _____________________________________________________________________________ (9) AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 5,952,772 _____________________________________________________________________________ (10) CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES [ ] _____________________________________________________________________________ (11) PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9) 4.0% _____________________________________________________________________________ (12) TYPE OF REPORTING PERSON OO _____________________________________________________________________________ Schedule 13G PAGE 4 of 20 CUSIP No. 723787107 _____________________________________________________________________________ (1) NAME OF REPORTING PERSON S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON Viking Global Equities LP _____________________________________________________________________________ (2) CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (a) [ ] (b) [x] _____________________________________________________________________________ (3) SEC USE ONLY _____________________________________________________________________________ (4) CITIZENSHIP OR PLACE OF ORGANIZATION Delaware _____________________________________________________________________________ NUMBER OF (5) SOLE VOTING POWER 0 SHARES ______________________________________________________________ BENEFICIALLY (6) SHARED VOTING POWER 2,029,551 OWNED BY ______________________________________________________________ EACH (7) SOLE DISPOSITIVE POWER 0 REPORTING ______________________________________________________________ PERSON WITH (8) SHARED DISPOSITIVE POWER 2,029,551 _____________________________________________________________________________ (9) AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 2,029,551 _____________________________________________________________________________ (10) CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES [ ] _____________________________________________________________________________ (11) PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9) 1.4% _____________________________________________________________________________ (12) TYPE OF REPORTING PERSON PN _____________________________________________________________________________ Schedule 13G PAGE 5 of 20 CUSIP No. 723787107 _____________________________________________________________________________ (1) NAME OF REPORTING PERSON S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON Viking Global Equities II LP _____________________________________________________________________________ (2) CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (a) [ ] (b) [x] _____________________________________________________________________________ (3) SEC USE ONLY _____________________________________________________________________________ (4) CITIZENSHIP OR PLACE OF ORGANIZATION Delaware _____________________________________________________________________________ NUMBER OF (5) SOLE VOTING POWER 0 SHARES ______________________________________________________________ BENEFICIALLY (6) SHARED VOTING POWER 120,039 OWNED BY ______________________________________________________________ EACH (7) SOLE DISPOSITIVE POWER 0 REPORTING ______________________________________________________________ PERSON WITH (8) SHARED DISPOSITIVE POWER 120,039 _____________________________________________________________________________ (9) AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 120,039 _____________________________________________________________________________ (10) CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES [ ] _____________________________________________________________________________ (11) PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9) 0.1% _____________________________________________________________________________ (12) TYPE OF REPORTING PERSON PN _____________________________________________________________________________ Schedule 13G PAGE 6 of 20 CUSIP No. 723787107 _____________________________________________________________________________ (1) NAME OF REPORTING PERSON S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON VGE III Portfolio Ltd. _____________________________________________________________________________ (2) CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (a) [ ] (b) [x] _____________________________________________________________________________ (3) SEC USE ONLY _____________________________________________________________________________ (4) CITIZENSHIP OR PLACE OF ORGANIZATION Cayman Islands _____________________________________________________________________________ NUMBER OF (5) SOLE VOTING POWER 0 SHARES ______________________________________________________________ BENEFICIALLY (6) SHARED VOTING POWER 3,803,182 OWNED BY ______________________________________________________________ EACH (7) SOLE DISPOSITIVE POWER 0 REPORTING ______________________________________________________________ PERSON WITH (8) SHARED DISPOSITIVE POWER 3,803,182 _____________________________________________________________________________ (9) AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 3,803,182 _____________________________________________________________________________ (10) CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES [ ] _____________________________________________________________________________ (11) PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9) 2.5% _____________________________________________________________________________ (12) TYPE OF REPORTING PERSON CO _____________________________________________________________________________ Schedule 13G PAGE 7 of 20 CUSIP No. 723787107 _____________________________________________________________________________ (1) NAME OF REPORTING PERSON S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON Viking Long Fund GP LLC _____________________________________________________________________________ (2) CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (a) [ ] (b) [x] _____________________________________________________________________________ (3) SEC USE ONLY _____________________________________________________________________________ (4) CITIZENSHIP OR PLACE OF ORGANIZATION Delaware _____________________________________________________________________________ NUMBER OF (5) SOLE VOTING POWER 0 SHARES ______________________________________________________________ BENEFICIALLY (6) SHARED VOTING POWER 2,321,581 OWNED BY ______________________________________________________________ EACH (7) SOLE DISPOSITIVE POWER 0 REPORTING ______________________________________________________________ PERSON WITH (8) SHARED DISPOSITIVE POWER 2,321,581 _____________________________________________________________________________ (9) AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 2,321,581 _____________________________________________________________________________ (10) CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES [ ] _____________________________________________________________________________ (11) PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9) 1.6% _____________________________________________________________________________ (12) TYPE OF REPORTING PERSON OO _____________________________________________________________________________ Schedule 13G PAGE 8 of 20 CUSIP No. 723787107 _____________________________________________________________________________ (1) NAME OF REPORTING PERSON S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON Viking Long Fund Master Ltd. _____________________________________________________________________________ (2) CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (a) [ ] (b) [x] _____________________________________________________________________________ (3) SEC USE ONLY _____________________________________________________________________________ (4) CITIZENSHIP OR PLACE OF ORGANIZATION Cayman Islands _____________________________________________________________________________ NUMBER OF (5) SOLE VOTING POWER 0 SHARES ______________________________________________________________ BENEFICIALLY (6) SHARED VOTING POWER 2,321,581 OWNED BY ______________________________________________________________ EACH (7) SOLE DISPOSITIVE POWER 0 REPORTING ______________________________________________________________ PERSON WITH (8) SHARED DISPOSITIVE POWER 2,321,581 _____________________________________________________________________________ (9) AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 2,321,581 _____________________________________________________________________________ (10) CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES [ ] _____________________________________________________________________________ (11) PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9) 1.6% _____________________________________________________________________________ (12) TYPE OF REPORTING PERSON CO _____________________________________________________________________________ Schedule 13G PAGE 9 of 20 CUSIP No. 723787107 _____________________________________________________________________________ (1) NAME OF REPORTING PERSON S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON Viking Global Opportunities GP LLC _____________________________________________________________________________ (2) CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (a) [ ] (b) [x] _____________________________________________________________________________ (3) SEC USE ONLY _____________________________________________________________________________ (4) CITIZENSHIP OR PLACE OF ORGANIZATION Delaware _____________________________________________________________________________ NUMBER OF (5) SOLE VOTING POWER 0 SHARES ______________________________________________________________ BENEFICIALLY (6) SHARED VOTING POWER 687,833 OWNED BY ______________________________________________________________ EACH (7) SOLE DISPOSITIVE POWER 0 REPORTING ______________________________________________________________ PERSON WITH (8) SHARED DISPOSITIVE POWER 687,833 _____________________________________________________________________________ (9) AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 687,833 _____________________________________________________________________________ (10) CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES [ ] _____________________________________________________________________________ (11) PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9) 0.5% _____________________________________________________________________________ (12) TYPE OF REPORTING PERSON OO _____________________________________________________________________________ Schedule 13G PAGE 10 of 20 CUSIP No. 723787107 _____________________________________________________________________________ (1) NAME OF REPORTING PERSON S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON Viking Global Opportunities Portfolio GP LLC _____________________________________________________________________________ (2) CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (a) [ ] (b) [x] _____________________________________________________________________________ (3) SEC USE ONLY _____________________________________________________________________________ (4) CITIZENSHIP OR PLACE OF ORGANIZATION Delaware _____________________________________________________________________________ NUMBER OF (5) SOLE VOTING POWER 0 SHARES ______________________________________________________________ BENEFICIALLY (6) SHARED VOTING POWER 687,833 OWNED BY ______________________________________________________________ EACH (7) SOLE DISPOSITIVE POWER 0 REPORTING ______________________________________________________________ PERSON WITH (8) SHARED DISPOSITIVE POWER 687,833 _____________________________________________________________________________ (9) AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 687,833 _____________________________________________________________________________ (10) CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES [ ] _____________________________________________________________________________ (11) PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9) 0.5% _____________________________________________________________________________ (12) TYPE OF REPORTING PERSON OO _____________________________________________________________________________ Schedule 13G PAGE 11 of 20 CUSIP No. 723787107 _____________________________________________________________________________ (1) NAME OF REPORTING PERSON S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON Viking Global Opportunities Liquid Portfolio Sub-Master LP _____________________________________________________________________________ (2) CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (a) [ ] (b) [x] _____________________________________________________________________________ (3) SEC USE ONLY _____________________________________________________________________________ (4) CITIZENSHIP OR PLACE OF ORGANIZATION Cayman Islands _____________________________________________________________________________ NUMBER OF (5) SOLE VOTING POWER 0 SHARES ______________________________________________________________ BENEFICIALLY (6) SHARED VOTING POWER 687,833 OWNED BY ______________________________________________________________ EACH (7) SOLE DISPOSITIVE POWER 0 REPORTING ______________________________________________________________ PERSON WITH (8) SHARED DISPOSITIVE POWER 687,833 _____________________________________________________________________________ (9) AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 687,833 _____________________________________________________________________________ (10) CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES [ ] _____________________________________________________________________________ (11) PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9) 0.5% _____________________________________________________________________________ (12) TYPE OF REPORTING PERSON PN _____________________________________________________________________________ Schedule 13G PAGE 12 of 20 CUSIP No. 723787107 _____________________________________________________________________________ (1) NAME OF REPORTING PERSON S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON O. Andreas Halvorsen _____________________________________________________________________________ (2) CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (a) [ ] (b) [x] _____________________________________________________________________________ (3) SEC USE ONLY _____________________________________________________________________________ (4) CITIZENSHIP OR PLACE OF ORGANIZATION Norway _____________________________________________________________________________ NUMBER OF (5) SOLE VOTING POWER 0 SHARES ______________________________________________________________ BENEFICIALLY (6) SHARED VOTING POWER 8,962,186 OWNED BY ______________________________________________________________ EACH (7) SOLE DISPOSITIVE POWER 0 REPORTING ______________________________________________________________ PERSON WITH (8) SHARED DISPOSITIVE POWER 8,962,186 _____________________________________________________________________________ (9) AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 8,962,186 _____________________________________________________________________________ (10) CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES [ ] _____________________________________________________________________________ (11) PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9) 6.0% _____________________________________________________________________________ (12) TYPE OF REPORTING PERSON IN _____________________________________________________________________________ Schedule 13G PAGE 13 of 20 CUSIP No. 723787107 _____________________________________________________________________________ (1) NAME OF REPORTING PERSON S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON David C. Ott _____________________________________________________________________________ (2) CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (a) [ ] (b) [x] _____________________________________________________________________________ (3) SEC USE ONLY _____________________________________________________________________________ (4) CITIZENSHIP OR PLACE OF ORGANIZATION United States _____________________________________________________________________________ NUMBER OF (5) SOLE VOTING POWER 0 SHARES ______________________________________________________________ BENEFICIALLY (6) SHARED VOTING POWER 8,962,186 OWNED BY ______________________________________________________________ EACH (7) SOLE DISPOSITIVE POWER 0 REPORTING ______________________________________________________________ PERSON WITH (8) SHARED DISPOSITIVE POWER 8,962,186 _____________________________________________________________________________ (9) AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 8,962,186 _____________________________________________________________________________ (10) CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES [ ] _____________________________________________________________________________ (11) PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9) 6.0% _____________________________________________________________________________ (12) TYPE OF REPORTING PERSON IN _____________________________________________________________________________ Schedule 13G PAGE 14 of 20 CUSIP No. 723787107 _____________________________________________________________________________ (1) NAME OF REPORTING PERSON S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON Daniel S. Sundheim _____________________________________________________________________________ (2) CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (a) [ ] (b) [x] _____________________________________________________________________________ (3) SEC USE ONLY _____________________________________________________________________________ (4) CITIZENSHIP OR PLACE OF ORGANIZATION United States _____________________________________________________________________________ NUMBER OF (5) SOLE VOTING POWER 0 SHARES ______________________________________________________________ BENEFICIALLY (6) SHARED VOTING POWER 8,962,186 OWNED BY ______________________________________________________________ EACH (7) SOLE DISPOSITIVE POWER 0 REPORTING ______________________________________________________________ PERSON WITH (8) SHARED DISPOSITIVE POWER 8,962,186 _____________________________________________________________________________ (9) AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 8,962,186 _____________________________________________________________________________ (10) CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES [ ] _____________________________________________________________________________ (11) PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9) 6.0% _____________________________________________________________________________ (12) TYPE OF REPORTING PERSON IN _____________________________________________________________________________ Schedule 13G PAGE 15 of 20 CUSIP No. 723787107 ITEM 1(a). NAME OF ISSUER: Pioneer Natural Resources Company ITEM 1(b). ADDRESS OF ISSUER'S PRINCIPAL EXECUTIVE OFFICES: 5205 N. O'Connor Blvd., Suite 200 Irving, Texas 75039 ITEM 2(a). NAME OF PERSON FILING: Viking Global Investors LP ("VGI"), Viking Global Performance LLC ("VGP"), Viking Global Equities LP ("VGE"), Viking Global Equities II LP ("VGEII"), VGE III Portfolio Ltd. ("VGEIII"), Viking Long Fund GP LLC ("VLFGP"), Viking Long Fund Master Ltd. ("VLFM"), Viking Global Opportunities GP LLC ("Opportunities GP"), Viking Global Opportunities Portfolio GP LLC ("Opportunities Portfolio GP"), Viking Global Opportunities Liquid Portfolio Sub-Master LP ("Opportunities Fund"), O. Andreas Halvorsen, David C. Ott and Daniel S. Sundheim (collectively, the "Reporting Persons") ITEM 2(b). ADDRESS OF PRINCIPAL OFFICE OR, IF NONE, RESIDENCE: The business address of each of the Reporting Persons is 55 Railroad Avenue, Greenwich, Connecticut 06830. ITEM 2(c). CITIZENSHIP: VGI, VGE and VGEII are Delaware limited partnerships; VGEIII and VLFM are Cayman Islands exempted companies; VGP, VLFGP, Opportunities GP and Opportunities Portfolio GP are Delaware limited liability companies; and Opportunities Fund is a Cayman Islands exempted limited partnership. O. Andreas Halvorsen is a citizen of Norway. David C. Ott and Daniel S. Sundheim are citizens of the United States. ITEM 2(d). TITLE OF CLASS OF SECURITIES: Common Stock ("Common Stock") ITEM 2(e). CUSIP NUMBER: 723787107 ITEM 3. IF THIS STATEMENT IS FILED PURSUANT TO 13d-1(b) OR 13d-2(b) OR (c), CHECK WHETHER THE PERSON FILING IS A: (a) [ ] Broker or dealer registered under Section 15 of the Act (b) [ ] Bank as defined in Section 3(a)(6) of the Act (c) [ ] Insurance Company as defined in Section 3(a)(19) of the Act (d) [ ] Investment Company registered under Section 8 of the Investment Company Act of 1940 (e) [ ] Investment Adviser registered under Section 203 of the Investment Advisers Act of 1940: see Rule 13d- 1(b)(1)(ii)(E) (f) [ ] Employee Benefit Plan, Pension Fund which is subject to the provisions of the Employee Retirement Income Security Act of 1974 or Endowment Fund; see Rule 13d- 1(b)(1)(ii)(F) Schedule 13G PAGE 16 of 20 CUSIP No. 723787107 (g) [ ] Parent Holding Company, in accordance with Rule 13d- 1(b)(ii)(G) (h) [ ] Savings Associations as defined in Section 3(b) of the Federal Deposit Insurance Act (i) [ ] Church Plan that is excluded from the definition of an investment company under Section 3(c)(14) of the Investment Company Act of 1940 (j) [ ] A non-U.S. institution in accordance with Rule 240.13d-1(b)(1)(ii)(J) (k) [ ] Group, in accordance with Rule 240.13d-1(b)(1)(ii)(K). If filing as a non-U.S. institution in accordance with Rule 240.13d-1(b)(1)(ii)(J), please specify the type of institution: ITEM 4. OWNERSHIP. A. VGI (a) Amount beneficially owned: 8,962,186 (b) Percent of class: 6.0% The percentages used herein and in this Item 4 are calculated based upon the Company's Form 10-Q for the quarterly period ended June 30, 2015 filed on August 7, 2015, which states that as of August 4, 2015 there were 149,307,983 shares of Common Stock outstanding. (c) Number of shares as to which such person has: (i) sole power to vote or to direct the vote 0 (ii) shared power to vote or to direct the vote 8,962,186 (iii) sole power to dispose or to direct the disposition of 0 (iv) shared power to dispose or to direct the disposition of 8,962,186 VGI provides managerial services to VGE, VGEII, VGEIII, VLFM and Opportunities Fund. VGI has the authority to dispose of and vote the shares of Common Stock. Based on Rule 13d-3 of the Securities Exchange Act of 1934, as amended (the "Act"), VGI may be deemed to beneficially own the shares of Common Stock directly held by VGE, VGEII, VGEIII, VLFM and Opportunities Fund. VGI does not directly own any shares of Common Stock. Schedule 13G PAGE 17 of 20 CUSIP No. 723787107 B. VGP (a) Amount beneficially owned: 5,952,772 (b) Percent of class: 4.0% (c) Number of shares as to which such person has: (i) sole power to vote or to direct the vote 0 (ii) shared power to vote or to direct the vote 5,952,772 (iii) sole power to dispose or to direct the disposition of 0 (iv) shared power to dispose or to direct the disposition of 5,952,772 VGP, as the general partner of VGE and VGEII, has the authority to dispose of and vote the shares of Common Stock directly owned by VGE and VGEII. VGP serves as investment manager to VGEIII and has the authority to dispose of and vote the shares of Common Stock directly owned by VGEIII. VGP does not directly own any shares of Common Stock. Based on Rule 13d-3 of the Act, VGP may be deemed to beneficially own the shares of Common Stock directly held by VGE, VGEII and VGEIII. C. VLFGP (a) Amount beneficially owned: 2,321,581 (b) Percent of class: 1.6% (c) Number of shares as to which such person has: (i) sole power to vote or to direct the vote 0 (ii) shared power to vote or to direct the vote 2,321,581 (iii) sole power to dispose or to direct the disposition of 0 (iv) shared power to dispose or to direct the disposition of 2,321,581 VLFGP serves as the investment manager of VLFM and has the authority to dispose of and vote the shares of Common Stock directly owned by VLFM. VLFGP does not directly own any shares of Common Stock. Based on Rule 13d-3 of the Act, VLFGP may be deemed to beneficially own the shares of Common Stock directly held by VLFM. D. Opportunities GP (a) Amount beneficially owned: 687,833 (b) Percent of class: 0.5% (c) Number of shares as to which such person has: (i) sole power to vote or to direct the vote 0 (ii) shared power to vote or to direct the vote 687,833 (iii) sole power to dispose or to direct the disposition of 0 (iv) shared power to dispose or to direct the disposition of 687,833 Opportunities GP serves as the sole member of Opportunities Portfolio GP and has the authority to dispose of and vote the shares of Common Stock controlled by Opportunities Portfolio GP, which consists of the shares of Common Stock directly held by Opportunities Fund. Opportunities GP does not directly own any shares of Common Stock. Based on Rule 13d-3 of the Act, Opportunities GP may be deemed to beneficially own the shares of Common Stock controlled by Opportunities Portfolio GP, which consists of the shares of Common Stock directly held by Opportunities Fund. E. Opportunities Portfolio GP (a) Amount beneficially owned: 687,833 (b) Percent of class: 0.5% (c) Number of shares as to which such person has: (i) sole power to vote or to direct the vote 0 (ii) shared power to vote or to direct the vote 687,833 (iii) sole power to dispose or to direct the disposition of 0 (iv) shared power to dispose or to direct the disposition of 687,833 Opportunities Portfolio GP serves as the general partner of Opportunities Fund and has the authority to dispose of and vote the shares of Common Stock directly owned by Opportunities Fund. Opportunities Portfolio GP does not directly own any shares of Common Stock. Based on Rule 13d-3 of the Act, Opportunities Portfolio GP may be deemed to beneficially own the shares of Common Stock directly held by Opportunities Fund. Schedule 13G PAGE 18 of 20 CUSIP No. 723787107 F. VGE (a) Amount beneficially owned: 2,029,551 (b) Percent of class: 1.4% (c) Number of shares as to which such person has: (i) sole power to vote or to direct the vote 0 (ii) shared power to vote or to direct the vote 2,029,551 (iii) sole power to dispose or to direct the disposition of 0 (iv) shared power to dispose or to direct the disposition of 2,029,551 VGE has the authority to dispose of and vote the shares of Common Stock directly owned by it, which power may be exercised by its general partner, VGP, and by VGI, an affiliate of VGP, which provides managerial services to VGE. G. VGEII (a) Amount beneficially owned: 120,039 (b) Percent of class: 0.1% (c) Number of shares as to which such person has: (i) sole power to vote or to direct the vote 0 (ii) shared power to vote or to direct the vote 120,039 (iii) sole power to dispose or to direct the disposition of 0 (iv) shared power to dispose or to direct the disposition of 120,039 VGEII has the authority to dispose of and vote the shares of Common Stock directly owned by it, which power may be exercised by its general partner, VGP, and by VGI, an affiliate of VGP, which provides managerial services to VGEII. H. VGEIII (a) Amount beneficially owned: 3,803,182 (b) Percent of class: 2.5% (c) Number of shares as to which such person has: (i) sole power to vote or to direct the vote 0 (ii) shared power to vote or to direct the vote 3,803,182 (iii) sole power to dispose or to direct the disposition of 0 (iv) shared power to dispose or to direct the disposition of 3,803,182 VGEIII has the authority to dispose of and vote the shares of Common Stock directly owned by it, which power may be exercised by its investment manager, VGP, and by VGI, an affiliate of VGP, which provides managerial services to VGEIII. Viking Global Equities III Ltd. (a Cayman Islands exempted company) invests substantially all of its assets through VGEIII. I. VLFM (a) Amount beneficially owned: 2,321,581 (b) Percent of class: 1.6% (c) Number of shares as to which such person has: (i) sole power to vote or to direct the vote 0 (ii) shared power to vote or to direct the vote 2,321,581 (iii) sole power to dispose or to direct the disposition of 0 (iv) shared power to dispose or to direct the disposition of 2,321,581 VLFM has the authority to dispose of and vote the shares of Common Stock directly owned by it, which power may be exercised by its investment manager, VLFGP, and by VGI, an affiliate of VLFGP, which provides managerial services to VLFM. Viking Long Fund LP (a Delaware limited partnership) and Viking Long Fund III Ltd. (a Cayman Islands exempted company), through its investment in Viking Long Fund Intermediate LP (a Cayman Islands limited partnership), invest substantially all of their assets through VLFM. J. Opportunities Fund (a) Amount beneficially owned: 687,833 (b) Percent of class: 0.5% (c) Number of shares as to which such person has: (i) sole power to vote or to direct the vote 0 (ii) shared power to vote or to direct the vote 687,833 (iii) sole power to dispose or to direct the disposition of 0 (iv) shared power to dispose or to direct the disposition of 687,833 Opportunities Fund has the authority to dispose of and vote the shares of Common Stock directly owned by it, which power may be exercised by its general partner, Opportunities Portfolio GP, and by VGI, an affiliate of Opportunities Portfolio GP, which provides managerial services to Opportunities Fund. Viking Global Opportunities LP (a Delaware limited partnership) and Viking Global Opportunities III LP (a Cayman Islands exempted limited partnership), through its investment in Viking Global Opportunities Intermediate LP (a Cayman Islands exempted limited partnership), invest substantially all of their assets in Viking Global Opportunities Master LP (a Cayman Islands exempted limited partnership), which in turn invests through Opportunities Fund. Schedule 13G PAGE 19 of 20 CUSIP No. 723787107 K. O. Andreas Halvorsen, David C. Ott and Daniel S. Sundheim (a) Amount beneficially owned: 8,962,186 (b) Percent of class: 6.0% (c) Number of shares as to which such person has: (i) sole power to vote or to direct the vote 0 (ii) shared power to vote or to direct the vote 8,962,186 (iii) sole power to dispose or to direct the disposition of 0 (iv) shared power to dispose or to direct the disposition of 8,962,186 Messrs. Halvorsen, Ott and Sundheim, as Executive Committee Members of VGI, VGP, VLFGP and Opportunities GP, have shared authority to dispose of and vote the shares of Common Stock beneficially owned by VGI, VGP, VLFGP and Opportunities GP. None of Messrs. Halvorsen, Ott and Sundheim directly owns any shares of Common Stock. Based on Rule 13d-3 of the Act, each may be deemed to beneficially own the shares of Common Stock directly held by VGE, VGE II, VGEIII, VLFM and Opportunities Fund. ITEM 5. OWNERSHIP OF FIVE PERCENT OR LESS OF A CLASS. If this statement is being filed to report the fact that as of the date hereof the Reporting Persons has ceased to be the beneficial owner of more than five percent of the class of securities, check the following.[] ITEM 6. OWNERSHIP OF MORE THAN FIVE PERCENT ON BEHALF OF ANOTHER PERSON. Yes, see Item 4. ITEM 7. IDENTIFICATION AND CLASSIFICATION OF THE SUBSIDIARY WHICH ACQUIRED THE SECURITY BEING REPORTED ON BY THE PARENT HOLDING COMPANY. Not applicable. ITEM 8. IDENTIFICATION AND CLASSIFICATION OF MEMBERS OF THE GROUP. Not applicable. ITEM 9. NOTICE OF DISSOLUTION OF GROUP. Not applicable. ITEM 10. CERTIFICATION. (if filing pursuant to Rule 13d-1(c)) By signing below each Reporting Person certifies that, to the best of its knowledge and belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and not held in connection with or as a participant in any transaction having that purpose or effect. Schedule 13G PAGE 20 of 20 CUSIP No. 723787107 SIGNATURES After reasonable inquiry and to the best of our knowledge and belief, the undersigned certify that the information set forth in this statement is true, complete and correct. DATED: October 30, 2015 /s/ O. ANDREAS HALVORSEN By: O. Andreas Halvorsen - individually and as an Executive Committee Member of VIKING GLOBAL PERFORMANCE LLC, on behalf of itself and VIKING GLOBAL EQUITIES LP, VIKING GLOBAL EQUITIES II LP and VGE III PORTFOLIO LTD., and as an Executive Committee Member of Viking Global Partners LLC, on behalf of VIKING GLOBAL INVESTORS LP, and as an Executive Committee Member of VIKING LONG FUND GP LLC, on behalf of itself and VIKING LONG FUND MASTER LTD., and as an Executive Committee Member of VIKING GLOBAL OPPORTUNITIES GP LLC, on behalf of itself and VIKING GLOBAL OPPORTUNITIES PORTFOLIO GP LLC and VIKING GLOBAL OPPORTUNITIES LIQUID PORTFOLIO SUB-MASTER LP /s/ DAVID C. OTT By: David C. Ott - individually and as an Executive Committee Member of VIKING GLOBAL PERFORMANCE LLC, on behalf of itself and VIKING GLOBAL EQUITIES LP, VIKING GLOBAL EQUITIES II LP and VGE III PORTFOLIO LTD., and as an Executive Committee Member of Viking Global Partners LLC, on behalf of VIKING GLOBAL INVESTORS LP, and as an Executive Committee Member of VIKING LONG FUND GP LLC, on behalf of itself and VIKING LONG FUND MASTER LTD., and as an Executive Committee Member of VIKING GLOBAL OPPORTUNITIES GP LLC, on behalf of itself and VIKING GLOBAL OPPORTUNITIES PORTFOLIO GP LLC and VIKING GLOBAL OPPORTUNITIES LIQUID PORTFOLIO SUB-MASTER LP /s/ DANIEL S. SUNDHEIM By: Daniel S. Sundheim - individually and as an Executive Committee Member of VIKING GLOBAL PERFORMANCE LLC, on behalf of itself and VIKING GLOBAL EQUITIES LP, VIKING GLOBAL EQUITIES II LP and VGE III PORTFOLIO LTD., and as an Executive Committee Member of Viking Global Partners LLC, on behalf of VIKING GLOBAL INVESTORS LP, and as an Executive Committee Member of VIKING LONG FUND GP LLC, on behalf of itself and VIKING LONG FUND MASTER LTD., and as an Executive Committee Member of VIKING GLOBAL OPPORTUNITIES GP LLC, on behalf of itself and VIKING GLOBAL OPPORTUNITIES PORTFOLIO GP LLC and VIKING GLOBAL OPPORTUNITIES LIQUID PORTFOLIO SUB-MASTER LP