SCHEDULE 13G

Under the Securities Exchange Act of 1934
(Amendment No. 5)*

PNM RESOURCES, INC.

(Name of Issuer)

Common Stock, no par value

(Title of Class of Securities)

744499104

(CUSIP Number)

December 31, 2008

(Date of Event Which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

*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).

(1) Cascade Investment, L.L.C. (“Cascade”) beneficially owns 7,019,550 shares of Common Stock of PNM Resources, Inc. (the “Issuer”), which is equivalent to 8.1% of the outstanding shares of Common Stock.  Pursuant to a Unit Purchase Agreement dated as of August 13, 2004, between the Issuer and Cascade, on November 17, 2008, Cascade purchased 477,800 shares of Series A Preferred Stock (the “Preferred Stock”) of the Issuer, which are convertible into 4,778,000 shares of Common Stock.  Certain regulatory and contractual approvals must be obtained prior to converting the Preferred Stock into shares of Common Stock if such conversion would result in Cascade owning 10% or more of the Issuer’s outstanding Common Stock.  It is not possible to know whether such approvals would be obtained within 60 days of being requested.  Cascade, could, however, without regulatory approval, convert a portion of the shares of Preferred Stock so long as the shares of Common Stock issued upon conversion of the Preferred Stock together with shares of Common Stock beneficially owned by Cascade prior to such conversion represent less than 10% of the outstanding Common Stock.  The number of shares reported in this report does not reflect any shares of Common Stock that Cascade would be entitled to receive upon conversion of the Preferred Stock without regulatory approval.

All Common Stock and Preferred Stock beneficially owned by Cascade may be deemed to be beneficially owned by William H. Gates III as the sole member of Cascade.  Michael Larson, the Business Manager of Cascade, has voting and investment power with respect to the Common Stock and Preferred Stock held by Cascade.  Mr. Larson disclaims any beneficial ownership of the Common Stock and Preferred Stock beneficially owned by Cascade and Mr. Gates.

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(1) Cascade Investment, L.L.C. (“Cascade”) beneficially owns 7,019,550 shares of Common Stock of PNM Resources, Inc. (the “Issuer”), which is equivalent to 8.1% of the outstanding shares of Common Stock.  Pursuant to a Unit Purchase Agreement dated as of August 13, 2004, between the Issuer and Cascade, on November 17, 2008, Cascade purchased 477,800 shares of Series A Preferred Stock (the “Preferred Stock”) of the Issuer, which are convertible into 4,778,000 shares of Common Stock.  Certain regulatory and contractual approvals must be obtained prior to converting the Preferred Stock into shares of Common Stock if such conversion would result in Cascade owning 10% or more of the Issuer’s outstanding Common Stock.  It is not possible to know whether such approvals would be obtained within 60 days of being requested.  Cascade, could, however, without regulatory approval, convert a portion of the shares of Preferred Stock so long as the shares of Common Stock issued upon conversion of the Preferred Stock together with shares of Common Stock beneficially owned by Cascade prior to such conversion represent less than 10% of the outstanding Common Stock.  The number of shares reported in this report does not reflect any shares of Common Stock that Cascade would be entitled to receive upon conversion of the Preferred Stock without regulatory approval.

All Common Stock and Preferred Stock beneficially owned by Cascade may be deemed to be beneficially owned by William H. Gates III as the sole member of Cascade.  Michael Larson, the Business Manager of Cascade, has voting and investment power with respect to the Common Stock and Preferred Stock held by Cascade.  Mr. Larson disclaims any beneficial ownership of the Common Stock and Preferred Stock beneficially owned by Cascade and Mr. Gates.

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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.

(1)  This amendment is being filed jointly by Cascade Investment, L.L.C. and William H. Gates III pursuant to the Joint Filing Agreement dated February 14, 2006 and included with the signature page to Amendment No. 3 to Schedule 13G with respect to PNM Resources, Inc. filed on February 14, 2006, SEC File No. 005-77986, and incorporated by reference herein.

(2)  Duly authorized under Special Power of Attorney appointing Michael Larson attorney-in-fact, dated February 3, 2006, by and on behalf of William H. Gates III, filed as Exhibit 99.1 to Cascade Investment, L.L.C.’s Amendment No. 2 to Schedule 13G with respect to Arch Capital Group Ltd. on March 7, 2006, SEC File No. 005-45257, and incorporated by reference herein.

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