SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 8)*

(Name of Issuer)

(Title of Class of Securities)

(CUSIP Number)

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

(Date of Event which Requires Filing of this Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of Rule 13d-1(e), 13d-1(f) or 13-1(g), check the following box  ¨.

Note. Schedules filed in paper format shall include a signed original and five copies of the schedule, including all exhibits. See Rule 13d-7 for other parties to whom copies are to be sent.

The information required on 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).

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This Amendment No. 8 amends the Schedule 13D (the “Original 13D”) filed with the Securities and Exchange Commission (“SEC”) on February 11, 2008 and as amended on August 12, 2008, September 12, 2008, October 6, 2008, October 14, 2008, October 17, 2008, October 22, 2008 and January 6, 2011. Unless otherwise stated herein, the Original 13D, as previously amended, remains in full force and effect. Terms used therein and not defined herein shall have the meanings ascribed thereto in the Original 13D.

Item 3 is hereby amended and restated in its entirety as follows:

The source and amount of the funds used or to be used by the Reporting Persons to purchase Shares are as follows:

Item 4 of the Original 13D, as amended, is hereby amended and supplemented by adding the following paragraph immediately following the second paragraph thereof:

As part of an overall assessment of their investment portfolio, the Reporting Persons are considering one or more further sales transactions in order to better align the size of their investment in the Issuer within their portfolio of investments and to monetize their investments in the Issuer. The Reporting Persons may effect this reduction of their investment positions in the Issuer through the sale of all or any part of their remaining Shares pursuant to Rule 144 under the Securities Act of 1933, as amended, in privately negotiated transactions, in registered sales (including pursuant to the exercise of their registration rights set forth in the Stockholder Agreement described in Item 6 below and filed as Exhibit C to this Amendment), or otherwise. Any such sales transactions by the Reporting Persons may be made at any time without additional prior notice.

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Item 5 is hereby amended and restated in its entirety as follows:

(a) Percentage interest calculations for each Reporting Person are based upon the Issuer having 481,367,880 total outstanding shares of Common Stock including 481,338,627 total shares of Common Stock reported on the Issuer’s annual report on Form 10-K filed with the Securities and Exchange Commission on February 10, 2012 and 29,253 total shares of restricted stock units granted to WEO and JSR in their respective capacities as members of the board of directors of the Issuer.

SPO

The aggregate number of Shares that SPO owns beneficially, pursuant to Rule 13d-3 of the Act, is 70,541,012 Shares, which constitutes approximately 14.7% of the outstanding Shares.

SPO Co-Investment

The aggregate number of Shares that SPO Co-Investment owns beneficially, pursuant to Rule 13d-3 of the Act, is 4,234,400 Shares, which constitutes approximately 0.9% of the outstanding Shares.

SPO Advisory Partners

Because of its position as the sole general partner of each of SPO and SPO Co-Investment, SPO Advisory Partners may, pursuant to Rule 13d-3 of the Act, be deemed to be the beneficial owner of 74,775,412 Shares, which constitutes approximately 15.5% of the outstanding Shares.

SFP

The aggregate number of Shares that SFP owns beneficially, pursuant to Rule 13d-3 of the Act, is 2,697,096 Shares, which constitutes approximately 0.6% of the outstanding Shares.

SF Advisory Partners

Because of its position as the sole general partner of SFP, SF Advisory Partners may, pursuant to Rule 13d-3 of the Act, be deemed to be the beneficial owner of 2,697,096 Shares, which constitutes approximately 0.6% of the outstanding Shares.

SPO Advisory Corp.

Because of its positions as the sole general partner of each of SPO Advisory Partners and SF Advisory Partners, SPO Advisory Corp. may, pursuant to Rule 13d-3 of the Act, be deemed to be the beneficial owner of 77,472,508 Shares in the aggregate, which constitutes approximately 16.1% of the outstanding Shares.

JHS

Individually, and because of his position as a control person of SPO Advisory Corp., and the controlling person, sole director and executive officer of PS Foundation, JHS may, pursuant to Rule 13d-3 of the Act, be deemed to be the beneficial owner of 77,619,008 Shares in the aggregate, which constitutes approximately 16.1% of the outstanding Shares.

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WEO

Individually, and because of his position as a control person of SPO Advisory Corp., WEO may, pursuant to Rule 13d-3 of the Act, be deemed to be the beneficial owner of 77,506,659 Shares in the aggregate, which constitutes approximately 16.1% of the outstanding Shares.

EHM

Individually, and because of his position as a control person of SPO Advisory Corp., EHM may, pursuant to Rule 13d-3 of the Act, be deemed to be the beneficial owner of 77,478,108 Shares, which constitutes approximately 16.1% of the outstanding Shares.

JSR

The aggregate number of Shares that JSR owns beneficially, pursuant to Rule 13d-3 of the Act, is 77,501,339, which constitutes approximately 16.1% of the outstanding Shares.

PS Foundation

The aggregate number of Shares that PS Foundation owns beneficially, pursuant to Rule 13d-3 of the Act, is 141,500 Shares, which constitutes less than 0.1% of the outstanding Shares.

To the best of the knowledge of each of the Reporting Persons, other than as set forth above, none of the persons named in Item 2 hereof is the beneficial owner of any Shares.

(b) SPO

Acting through its sole general partner, SPO has the sole power to vote or to direct the vote and to dispose or to direct the disposition of 70,541,012 Shares.

SPO Co-Investment

Acting through its sole general partner, SPO Co-Investment has the sole power to vote or to direct the vote and to dispose or to direct the disposition of 4,234,400 Shares.

SPO Advisory Partners

Acting through its sole general partner and in its capacity as the sole general partner of each of SPO and SPO Co-Investment, SPO Advisory Partners has the sole power to vote or to direct the vote and to dispose or to direct the disposition of 74,775,412 Shares.

SFP

Acting through its sole general partner, SFP has the sole power to vote or to direct the vote and to dispose or to direct the disposition of 2,697,096 Shares.

SF Advisory Partners

Acting through its sole general partner and in its capacity as the sole general partner of SFP, SF Advisory Partners has the sole power to vote or to direct the vote and to dispose or to direct the disposition of 2,697,096 Shares.

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SPO Advisory Corp.

Acting through its controlling persons and through JSR in his advisory capacity, and in its capacities as the sole general partner of each of SPO Advisory Partners and SF Advisory Partners, SPO Advisory Corp. may be deemed to have shared power with JSR to vote or to direct the vote and to dispose or to direct the disposition of 77,472,508 Shares in the aggregate.

JHS

As one of three controlling persons of SPO Advisory Corp., which is the sole general partner of each of SPO Advisory Partners and SF Advisory Partners, JHS may be deemed to have shared power with WEO and EHM to vote or to direct the vote and to dispose or to direct the disposition of 77,472,508 Shares held by SPO, SPO Co-Investment and SFP in the aggregate. In addition, JHS has the sole power to vote or to direct the vote and to dispose or to direct the disposition of 5,000 Shares held in the John H. Scully Individual Retirement Accounts, which are self-directed individual retirement accounts, and 141,500 Shares held by the PS Foundation, for which JHS is the controlling person, sole director and executive officer.

WEO

As one of three controlling persons of SPO Advisory Corp., which is the sole general partner of each of SPO Advisory Partners and SF Advisory Partners, WEO may be deemed to have shared power with JHS and EHM to vote or to direct the vote and to dispose or to direct the disposition of 77,472,508 Shares held by SPO, SPO Co-Investment and SFP in the aggregate. In addition, WEO has the sole power to vote or to direct the vote and to dispose or to direct the disposition of 28,700 Shares held in the William E. Oberndorf Individual Retirement Account, which is a self-directed individual retirement account, and 5,451 Shares of restricted stock awarded to WEO in his capacity as director of Issuer.

EHM

As one of three controlling persons of SPO Advisory Corp., which is the sole general partner of each of SPO Advisory Partners and SF Advisory Partners, EHM may be deemed to have shared power with JHS and WEO to vote or to direct the vote and to dispose or to direct the disposition of 77,472,508 Shares held by SPO, SPO Co-Investment and SFP in the aggregate. In addition, EHM has the sole power to vote or to direct the vote and to dispose or to direct the disposition of 5,600 Shares held in the Edward H. McDermott Individual Retirement Account, which is a self-directed individual retirement account.

JSR

Because of his advisory position in SPO Advisory Corp., which is the sole general partner of each of SPO Advisory Partners and SF Advisory Partners, JSR may be deemed to have shared power with SPO Advisory Corp. to dispose or to direct the disposition of 77,472,508 Shares held by SPO, SPO Co-Investment and SFP in the aggregate. In addition, JSR has the sole power to vote or to direct the vote and to dispose or to direct the disposition of 28,831 Shares of restricted stock awarded to JSR in his capacity as a director of the Issuer.

PS Foundation

Acting through its controlling person, PS Foundation has the sole power to vote or to direct the vote and to dispose or to direct the disposition of 141,500 Shares.

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(c) Since the most recent filing on Schedule 13D, Reporting Persons have acquired Shares through the distribution of Shares pursuant to the Issuer’s Chapter 11 plan of reorganization and WEO and JSR have received 5,451 and 8,479 Shares, respectively, through the vesting of their respective restricted stock units. On February 13, 2012, the Reporting Persons sold an aggregate of 16,800,000 Shares in a block trade at a price of $15.57 per share.

(d) Each of the Reporting Persons affirms that no person other than such Reporting Person has the right to receive or the power to direct the receipt of distributions with respect to, or the proceeds from the sale of, Shares owned by such Reporting Persons.

Item 6 of the Original 13D, as amended, is hereby amended and supplemented by inserting the following paragraph immediately following the first paragraph thereof:

SPO and SFP are party to the Registration Rights Agreement, pursuant to which the Issuer has granted to SPO, SFP and the other shareholders party thereto, customary demand and piggyback registration rights relating to the Issuer’s common stock, which SPO and SFP may exercise for so long as they, together with their affiliates, own at least 25% of the registrable securities held by them on the date of the Registration Rights Agreement.

Pursuant to the terms of the Registration Rights Agreement and subject to certain customary exceptions, each of SPO and SFP may request up to two registrations of underwritten offerings of all or any portion of their registrable securities; provided, that any such demand may only be exercised if the total offering price of the shares to be sold in such offering, including piggyback shares (before deduction for underwriting discounts), exceeds $100 million.

The description of the Registration Rights Agreement above is not intended to be complete and is qualified in its entirety by the terms of the Registration Rights Agreement filed as an Exhibit to this Schedule 13D.

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SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Dated: February 13, 2012

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INDEX OF EXHIBITS