EXHIBIT 99.13

                    TARGETED GROWTH ENHANCED TERMS SECURITIES

                                TARGETS TRUST XX

                        SUPPLEMENTAL GUARANTEE AGREEMENT

                            Dated as of June 30, 2005



            THIS SUPPLEMENTAL TARGETS GUARANTEE AGREEMENT (the "Supplemental
Guarantee Agreement") dated as of June 30, 2005 is executed and delivered by
Citigroup Global Markets Holdings Inc., a New York corporation ("CGMHI"),
Citigroup Inc., a Delaware corporation ("Citigroup"), and JPMorgan Chase Bank,
N.A., a national banking association, as trustee (the "TARGETS Guarantee
Trustee"), for the benefit of the Holders (as defined herein) from time to time
of the TARGETS (as defined herein) of TARGETS Trust XX, a Delaware statutory
trust (the "Issuer").

            WHEREAS, pursuant to an Amended and Restated Declaration of Trust
dated as of February 26, 2004 among the trustees of the Issuer named therein,
CGMHI, as sponsor, and the holders from time to time of undivided beneficial
interests in the assets of the Issuer, the Issuer issued on that date 5,500,000
preferred securities designated the Targeted Growth Enhanced Terms Securities
(the "TARGETS");

            WHEREAS, pursuant to a TARGETS Guarantee Agreement (the
"Agreement"), dated as of February 26, 2004 between CGMHI and the TARGETS
Guarantee Trustee, CGMHI agreed to pay to the Holders the Guarantee Payments (as
defined therein) with respect to the TARGETS and to make certain other payments
on the terms and conditions set forth therein;

            WHEREAS, Citigroup desires to fully and unconditionally guarantee,
as set forth herein, the Guarantee Payments; and

            WHEREAS, the execution of the Supplemental Guarantee Agreement is
authorized and permitted by Section 8.2 of the Agreement and all conditions
precedent provided for in the Agreement relating to the execution of the
Supplemental Guarantee Agreement have been complied with;

            NOW, THEREFORE, THIS SUPPLEMENTAL GUARANTEE AGREEMENT WITNESSETH:
That in order to effectuate the guarantee described herein, Citigroup agrees
with CGMHI and the TARGETS Guarantee Trustee, for the equal and proportionate
benefit of the respective holders from time to time of the TARGETS (the
"Holders"), as follows:

                                    ARTICLE I
                               Citigroup Guarantee

            Citigroup does hereby fully and unconditionally guarantee (the
"Citigroup Guarantee") to the Holders the Guarantee Payments when due, in
accordance with the provisions of the Agreement, as provided below:

            SECTION I.1. Notice of acceptance of the Citigroup Guarantee and of
default of performance by CGMHI is expressly waived, and payment under the
Citigroup Guarantee shall be subject to no condition other than the giving of a
written request for payment in accordance with the provisions of the Indenture,
stating the fact of default of performance, mailed to Citigroup at the following
address: Citigroup Inc., Office of Corporate Treasury, 153 East 53rd Street, 6th
Floor, New York, New York 10043, Attention: Treasurer. This Citigroup Guarantee
is a guarantee of payment and not of collection.



            SECTION I.2. The right of the Holders under any debt instrument of
CGMHI that is outstanding as of the date hereof to claim payment from Citigroup
under the Citigroup Guarantee shall rank in priority of payment with Citigroup's
other obligations to exactly the same extent that the Guarantee Payments rank
with CGMHI's other obligations, if any.

            SECTION I.3. The obligations of Citigroup under the Citigroup
Guarantee shall in no way be impaired by: (1) any extension, amendment,
modification or renewal of the TARGETS; (2) any waiver of any event of default,
extension of time or failure to enforce any of the TARGETS; or (3) any
extension, moratorium or other relief granted to CGMHI pursuant to any
applicable law or statute.

            SECTION I.4. Citigroup shall be obligated to make payment under the
Citigroup Guarantee, for the benefit of the Holders, at the same address as
CGMHI is obligated to make payment.

            SECTION I.5. (a) Subject to clause (b) below, Citigroup hereby
agrees that the Guarantee Payments will be paid strictly in accordance with the
terms of the Agreement, regardless of the value, genuineness, validity,
regularity or enforceability of the TARGETS. Subject to clause (b) below, the
liability of Citigroup to the extent herein set forth shall be absolute and
unconditional, not subject to any reduction, limitation, impairment,
termination, defense, offset, counterclaim or recoupment whatsoever (all of
which are hereby expressly waived by Citigroup) whether by reason of any claim
of any character whatsoever, including, without limitation, any claim of waiver,
release, surrender, alteration or compromise, or by reason of any liability at
any time to Citigroup or otherwise, whether based upon any obligations or any
other agreement or otherwise, and howsoever arising, whether out of action or
inaction or otherwise and whether resulting from default, willful misconduct,
negligence or otherwise, and without limiting the foregoing, irrespective of:

            (i) any lack of validity or enforceability of any agreement or
      instrument relating to the TARGETS;

            (ii) any change in the time, manner or place of payment of, or in
      any other term in respect of, all or any of the TARGETS, or any other
      amendment or waiver of or consent to any departure from any other
      agreement relating to any TARGETS;

            (iii) any increase in, addition to, exchange or release of, or
      nonperfection of any lien on or security interest in, any collateral, or
      any release or amendment or waiver of or consent to any departure from or
      failure to enforce any other guarantee, for all or any of the
      indebtedness;

            (iv) any other circumstance which might otherwise constitute a
      defense available to, or a discharge of, CGMHI in respect of the TARGETS;

            (v) the absence of any action on the part of the TARGETS Guarantee
      Trustee to obtain payment of the TARGETS from CGMHI;

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            (vi) any insolvency, bankruptcy, reorganization or dissolution, or
      any similar proceeding of CGMHI, including, without limitation, rejection
      of the TARGETS in such bankruptcy; or

            (vii) the absence of notice or any delay in any action to enforce
      any TARGETS or to exercise any right or remedy against Citigroup, or
      CGMHI, whether hereunder, under any TARGETS or any agreement or any
      indulgence, compromise or extension granted.

      (b) Notwithstanding anything to the contrary in this Citigroup Guarantee,
Citigroup does not waive any defense that would be available to CGMHI based on,
among other things, a breach, default or misrepresentation by the TARGETS
Guarantee Trustee, or failure of any condition to CGMHI's obligations under the
Agreement or the illegality of any provision of the Agreement.

            SECTION I.6. Citigroup further agrees that, to the extent that CGMHI
or Citigroup makes a payment or payments to the TARGETS Guarantee Trustee, which
payment or payments or any part thereof are subsequently invalidated, declared
to be fraudulent or preferential, set aside and/or required to be repaid to
CGMHI or Citigroup or their respective estate, trustee, receiver or any other
party under any bankruptcy law, state or federal law, common law or equitable
cause, then to the extent of such payment or repayment, this Citigroup Guarantee
and the advances or part thereof which have been paid, reduced or satisfied by
such amount shall be reinstated and continued in full force and effect as of the
date such initial payment, reduction or satisfaction occurred.

            SECTION I.7. Until the TARGETS are paid in full, Citigroup shall
have no rights (direct or indirect) of subrogation, contribution, reimbursement,
indemnification, or other rights of payment or recovery from CGMHI for any
payments made by Citigroup hereunder.

            SECTION I.8. This Citigroup Guarantee shall be binding upon and
shall inure to the benefit of the parties hereto and their respective successors
and assigns, including, without limitation, the Trustee.

                                   ARTICLE II
                            Miscellaneous Provisions

            SECTION II.1. This Supplemental Guarantee Agreement is executed and
shall be construed as an amendment to the Agreement, and forms a part thereof.
Except as herein expressly otherwise defined, the use of the terms and
expressions herein is in accordance with the definitions, uses and constructions
contained in the Agreement. Except as expressly amended hereby, the Agreement
shall continue in full force and effect in accordance with the provisions
thereof and the Agreement is in all respects hereby ratified and confirmed.

            SECTION II.2. The recitals herein and in the Agreement shall be
taken as the statements of CGMHI and Citigroup, and the TARGETS Guarantee
Trustee assumes no responsibility for the correctness thereof. The TARGETS
Guarantee Trustee makes no representations as to the validity or sufficiency of
this Supplemental Guarantee Agreement or of the Agreement. The TARGETS Guarantee
Trustee makes no undertakings or representations in

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respect of, and shall not be responsible in any manner whatsoever for and in
respect of, the validity or sufficiency of this Supplemental Guarantee Agreement
or the proper authorization or the due execution hereof by CGMHI or Citigroup or
for or in respect of the recitals and statements contained herein, all of which
recitals and statements are made solely by CGMHI and Citigroup.

            SECTION II.3. All of the covenants, stipulations, premises and
agreements made in this Supplemental Guarantee Agreement by CGMHI and Citigroup
shall bind their respective successors and assigns whether so expressed or not.

            SECTION II.4. This Supplemental Guarantee Agreement shall be deemed
to be a contract made under the laws of the State of New York and for all
purposes shall be construed in accordance with the laws of said State.

            SECTION II.5. This Supplemental Guarantee Agreement may be executed
in any number of counterparts, each of which when so executed shall be deemed to
be an original, but all such counterparts shall together constitute but one and
the same instrument.

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

                                             CITIGROUP GLOBAL MARKETS HOLDINGS
                                                 INC.

                                             By: /s/ Geoffrey S. Richards
                                                 -------------------------------
                                                 Name: Geoffrey S. Richards
                                                 Title: Vice President

                                             CITIGROUP INC.

                                             By: /s/ Charles E. Wainhouse
                                                 -------------------------------
                                                 Name: Charles E. Wainhouse
                                                 Title: Assistant Treasurer

                                             JPMORGAN CHASE BANK, N.A., as
                                                 TARGETS Guarantee Trustee

                                             By: /s/ Thomas Venusti
                                                 -------------------------------
                                                 Name: Thomas Venusti
                                                 Title: Assistant Vice President