**Exhibit
      4a**




FIRST
      SUPPLEMENTAL INDENTURE, dated as of October 5, 2007, to the Indenture dated
      as
      of November 1, 2004 (as amended and supplemented to the date hereof, the
“Indenture”), by and between TXU Corp., a Texas corporation (the “Company”) and
      The Bank of New York, as trustee (the “Trustee”).




W
      I T N E S S E T H:




WHEREAS,
      the Company and the Trustee have heretofore executed and delivered the
      Indenture, and the Company has issued pursuant to the Indenture its 4.80% Series
      O Senior Notes due 2009 (the “Notes”);




WHEREAS,
      Section 1202 of the Indenture provides that the Company and the Trustee may,
      with the consents of the holders of at least a majority in aggregate principal
      amount of the Securities (as defined in the Indenture) of all series Outstanding
      (as defined in the Indenture) under the Indenture, considered as one class,
      enter into this Supplemental Indenture;




WHEREAS,
      the Notes are the only Securities Outstanding under the Indenture;




WHEREAS,
      the Company has offered to purchase for cash, among other securities, any and
      all of the outstanding Notes upon the terms and subject to the conditions set
      forth in the Offer to Purchase and Consent Solicitation Statement, dated
      September 25, 2007 (as the same may be amended or supplemented from time to
      time, the “Statement”), and in the related Consent and Letter of Transmittal (as
      the same may be amended or supplemented from time to time, and, together with
      the Statement, the “Offer”), from each Holder of such Notes;




WHEREAS,
      the Offer is conditioned upon, among other things, certain amendments to the
      Indenture, to the Officer’s Certificate dated November 26, 2004 relating to the
      Notes (the “2004 Officer’s Certificate”) and to the Notes set forth in Article
      Two, Article Three, Article Four and Article Five of this Supplemental Indenture
      (the “Amendments”) having been approved by Holders of not less than a majority
      of the outstanding principal amount of the Notes and a supplemental indenture
      in
      respect thereof having been executed and delivered by the Company and the
      Trustee;




WHEREAS,
      the Company has received the consents from Holders of not less than a majority
      of the outstanding aggregate principal amount of the Notes to effect the
      Amendments;




WHEREAS,
      the Company has delivered to the Trustee an Officer’s Certificate (as defined in
      the Indenture) as well as an Opinion of Counsel (as defined in the Indenture)
      to
      the effect that the execution and delivery of this Supplemental Indenture by
      the
      Company is authorized or permitted under the Indenture and that all conditions
      precedent provided for in the Indenture to the execution and delivery of this
      Supplemental Indenture to be complied with by the Company have been complied
      with;




WHEREAS,
      the Company has been authorized by resolution to enter into this Supplemental
      Indenture;












WHEREAS,
      all other acts and proceedings required by law, by the Indenture and by the
      charter documents of the Company to make this Supplemental Indenture a valid
      and
      binding agreement for the purposes expressed herein, in accordance with its
      terms, have been duly done and performed; and




WHEREAS,
      the Company hereby requests that the Trustee execute and deliver this
      Supplemental Indenture;




NOW,
      THEREFORE, in consideration of the premises and the covenants and agreements
      contained herein, and for other good and valuable consideration the receipt
      of
      which is hereby acknowledged, the Company and the Trustee hereby agree as
      follows:




ARTICLE
      ONE


SECTION
      1.01.Definitions




.




Capitalized
      terms used in this Supplemental Indenture and not otherwise defined herein
      shall
      have the meanings assigned to such terms in the Indenture.




ARTICLE
      TWO


SECTION
      2.01.Amendments to Table of Contents




.




(a)           The
      Table of Contents of the Indenture is amended by deleting the titles to Sections
      602, 605, 606, 608 and 815 and inserting in lieu thereof the phrase
“[intentionally omitted]”.




(b)           The
      Table of Contents of the Indenture is further amended by deleting the title
      to
      Section 1002 and replacing it with the following: “REPORTS BY
      TRUSTEE”.




ARTICLE
      THREE


SECTION
      3.01.Elimination of Certain Provisions in Article
      Six




.




(a)           Section
      602 of the Indenture is amended by deleting it in its entirety and inserting
      in
      lieu thereof the phrase “[intentionally omitted]”.




(b)           Section
      605 of the Indenture is amended by deleting it in its entirety and inserting
      in
      lieu thereof the phrase “[intentionally omitted]”.




(c)           Section
      606 of the Indenture is amended by deleting it in its entirety and inserting
      in
      lieu thereof the phrase “[intentionally omitted]”.




(d)           Section
      608 of the Indenture is amended by deleting it in its entirety and inserting
      in
      lieu thereof the phrase “[intentionally omitted]”.

















SECTION
      3.02.Elimination of Certain Provisions in Article
      Eight




.




(a)           Section
      801 of the Indenture is amended by deleting the text of subsection (c) in its
      entirety and inserting in lieu thereof the phrase “[intentionally
      omitted]”.




(b)           Section
      815 of the Indenture is amended by deleting it in its entirety and inserting
      in
      lieu thereof the phrase “[intentionally omitted]”.




.


SECTION 3.03.Amendment and Elimination of Certain
        Provisions in Article Ten




(a)           Section
      1002 of the Indenture is amended by deleting the final two sentences of the
      first paragraph and the entire second paragraph of this section.




(b)           Section
      1002 of the Indenture is further amended by retitling such section as “Section
      1002.  REPORTS BY TRUSTEE”.




.


SECTION 3.04.Amendment and Elimination of Certain
        Provisions in Article Eleven




(a)           Section
      1101 of the Indenture is amended by deleting subsections (b) and (c) and
      inserting in lieu thereof the phrase “[intentionally omitted]”.




ARTICLE
      FOUR




.


SECTION 4.01.Amendment of a Provision in the 2004
        Officer’s Certificate






The
      2004 Officer’s Certificate is amended by deleting Section 13 in its entirety and
      inserting in lieu thereof the phrase “[intentionally omitted]”.







ARTICLE
      FIVE


SECTION
      5.01.Amendment of Certain Provisions in the
      Notes




.




The
      Notes are amended by inserting the following text on the reverse of each
      Note:




“Notwithstanding
      anything to the contrary contained herein, the terms of the Indenture, the
      related Officer’s Certificate and this Security have been amended and the
      following provisions of the Indenture and the related Officer’s Certificate, and
      the corresponding provisions of this Security, are no longer applicable to
      this
      Security:  Section 602, Section 605, Section 606, Section 608,
      subsection (c) of Section 801, Section 815 and subsections (b) and (c) of
      Section 1101; and Section 13 of the Officer’s Certificate.  In
      addition, Section 1002 of the Indenture has been amended.”












ARTICLE
      SIX


SECTION
      6.01.Effectiveness of Amendments




.




This
      Supplemental Indenture shall be effective upon its execution and delivery by
      the
      parties hereto. The Amendments set forth in Articles Two through Five hereof
      will only become operative immediately prior to the acceptance for payment
      of
      Notes validly tendered and not withdrawn at or prior to the Consent Payment
      Deadline (as defined in the Statement) pursuant to the Offer
      therefor.




SECTION
      6.02.Continuing Effect of Indenture




.




Except
      as expressly provided herein, all of the terms, provisions and conditions of
      the
      Indenture, the Notes and the 2004 Officer’s Certificate shall remain in full
      force and effect.




SECTION
      6.03.Construction of Supplemental
      Indenture




.




This
      Supplemental Indenture is executed as and shall constitute an indenture
      supplemental to the Indenture and shall be construed in connection with and
      as
      part of the Indenture.  THE LAWS OF THE STATE OF NEW YORK SHALL GOVERN
      AND BE USED TO CONSTRUE THIS SUPPLEMENTAL INDENTURE.




SECTION
      6.04.Trust
      Indenture Act Controls




.




If
      any provision of this Supplemental Indenture limits, qualifies or conflicts
      with
      another provision of this Supplemental Indenture or the Indenture that is
      required to be included by the Trust Indenture Act of 1939 as in force at the
      date as of which this Supplemental Indenture is executed, the provision required
      by said Act shall control.




SECTION
      6.05.Trustee Disclaimer




.




The
      recitals and statements contained in this Supplemental Indenture shall be taken
      as the recitals and statements of the Company, and the Trustee assumes no
      responsibility for their correctness.  The Trustee makes no
      representations as to the validity or sufficiency of this Supplemental
      Indenture.  All rights, protections, privileges, indemnities and
      benefits granted or afforded to the Trustee under the Indenture shall be deemed
      incorporated herein by this reference and shall be deemed applicable to all
      actions taken, suffered or omitted by the Trustee under this Supplemental
      Indenture.




SECTION
      6.06.Counterparts




.




This
      Supplemental Indenture may be executed in any number of counterparts, each
      of
      which so executed shall be deemed to be an original, but all such counterparts
      shall together constitute but one and the same instrument.

















SECTION
      6.07.Supplemental Indenture Forms Part of
      Indenture




.




This
      Supplemental Indenture is executed and shall be construed as an indenture
      supplemental to the Indenture and, as provided in the Indenture, this
      Supplemental Indenture forms a part of the Indenture for all
      purposes.  The Indenture, as amended and supplemented by this
      Supplemental Indenture, is in all respects ratified and confirmed.




SECTION
      6.08.Headings




.




The
      section headings herein are for convenience only and shall not affect the
      construction hereof.




SECTION
      6.09.Severability




.




In
      case any provision in this Supplemental Indenture, the 2004 Officer’s
      Certificate or the Notes shall be invalid, illegal or unenforceable, the
      validity, legality and enforceability of the remaining provisions shall not
      in
      any way be affected or impaired thereby.












IN
      WITNESS WHEREOF, the parties hereto have caused this Supplemental Indenture
      to
      be duly executed, all as of the day and year first above written.




TXU
                CORP.By:Name:Title:THE
                BANK OF NEW YORK,
              as
                TrusteeBy:Name:Title:







TXU
                CORP.By:Name:Title:THE
                BANK OF NEW YORK,
              as
                TrusteeBy:Name:Title: