GUARANTEE AGREEMENT

Exhibit 4.5

Execution Copy

G UARANTEE A GREEMENT

by and between

WELLS FARGO & COMPANY

as Guarantor

and

THE BANK OF NEW YORK MELLON TRUST COMPANY, NATIONAL ASSOCIATION

as Guarantee Trustee

relating to

WELLS FARGO CAPITAL XV

Dated as of September 10, 2008

CROSS-REFERENCE TABLE ^*

T ABLE OF C ONTENTS

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This G UARANTEE A GREEMENT , dated as of September 10, 2008, is executed and delivered by W ELLS F ARGO  & C OMPANY , a Delaware corporation (the “ Guarantor ”), having its principal office at 420 Montgomery Street, San Francisco, California 94163, and T HE B ANK OF N EW Y ORK M ELLON T RUST C OMPANY , N ATIONAL A SSOCIATION , a national banking association organized and existing under the laws of the United States, as trustee (the “ Guarantee Trustee ”), for the benefit of the Holders (as defined herein) from time to time of the Trust Preferred Securities of Wells Fargo Capital XV, a Delaware statutory trust (the “ Issuer Trust ”).

WHEREAS , pursuant to an Amended and Restated Trust Agreement, dated as of September 10, 2008 (the “ Trust Agreement ”), among the Guarantor, as Depositor, The Bank of New York Mellon Trust Company, National Association, as Property Trustee for the Issuer Trust (the “ Property Trustee ”), BNY Mellon Trust of Delaware, as Delaware Trustee for the Issuer Trust (the “ Delaware Trustee ”), each of the individuals set forth therein in their capacity as Administrative Trustee for the Issuer Trust (each, an “ Administrative Trustee ,” and together, the “ Administrative Trustees ”) and the Holders from time to time of the Trust Securities, the Issuer Trust is issuing $1,750,000,000 aggregate Liquidation Amount of Trust Preferred Securities having the terms set forth in the Trust Agreement on the date hereof and may from time to time after the execution of the Trust Agreement up to and including the 13th day following the Time of Delivery, issue additional Trust Preferred Securities having the same terms.

WHEREAS , the proceeds of the Trust Preferred Securities will be used to purchase the Notes, which initially will be pledged by the Issuer Trust, acting through the Property Trustee, to Wilmington Trust Company, as Collateral Agent for the Guarantor, pursuant to the Collateral Agreement, dated as of the date hereof, among the Guarantor, Wilmington Trust Company, as Collateral Agent, Custodial Agent, Securities Intermediary and Securities Registrar, and the Issuer Trust (acting through the Property Trustee).

WHEREAS , as an incentive for the Holders to purchase the Trust Preferred Securities, the Guarantor desires irrevocably and unconditionally to agree, to the extent set forth herein, to pay to the Holders of the Trust Preferred Securities the Guarantee Payments (as defined herein) and to make certain other payments on the terms and conditions set forth herein.

NOW, THEREFORE, in consideration of the purchase of Trust Preferred Securities by each Holder, which purchase the Guarantor hereby agrees shall benefit the Guarantor, the Guarantor executes and delivers this Guarantee Agreement for the benefit of the Holders from time to time.

ARTICLE I

Definitions

Section 1.1 Definitions.

As used in this Guarantee Agreement, the terms set forth below shall, unless the context otherwise requires, have the following meanings. Capitalized or otherwise defined terms used but not otherwise defined herein shall have the meanings assigned to such terms in the Trust Agreement as in effect on the date hereof.

“ Affiliate ” of any specified Person means any other Person directly or indirectly controlling or controlled by or under direct or indirect common control with such specified Person; provided , however , that an Affiliate of the Guarantor shall not be deemed to be an Affiliate of the Issuer Trust. For the purposes of this definition, “control” when used with respect to any specified Person means the power to direct the management and policies of such Person, directly or indirectly, whether through the ownership of voting securities, by contract or otherwise; and the terms “controlling” and “controlled” have meanings correlative to the foregoing.

“ Board of Directors ” means the board of directors of the Guarantor or any committee of that board duly authorized to act hereunder.

“ Event of Default ” means a default by the Guarantor on any of its payment or other obligations under this Guarantee Agreement; provided , however , that, except with respect to a default in payment of any Guarantee Payments, the Guarantor shall have received notice of default and shall not have cured such default within 30 days after receipt of such notice.

“ Guarantee Agreement ” means this Guarantee Agreement, as modified, amended or supplemented from time to time.

“ Guarantee Payments ” means the following payments or distributions, without duplication, with respect to the Trust Preferred Securities of any Series, to the extent not paid or made by or on behalf of the Issuer Trust (other than withholding and backup withholding tax): (i) any accumulated and unpaid Distributions required to be paid on the Trust Preferred Securities of such Series, to the extent the Issuer Trust shall have funds on hand available therefor at such time; (ii) the Redemption Price with respect to any Trust Preferred Securities called for redemption by the Issuer Trust (other than in connection with the redemption of Capital PPS in exchange for Notes or, if the Company elects to remarket the Notes in the form of New Trust Preferred Securities pursuant to Section 3.2(f) of the Indenture Supplement, such New Trust Preferred Securities), to the extent the Issuer Trust shall have funds on hand available therefor at such time; and (iii) upon a voluntary or involuntary termination, winding-up or liquidation of the Issuer Trust, other than in connection with the distribution of a Like Amount of Corresponding Assets to the Holders of Trust Preferred Securities and Common Securities, the lesser of (a) the Liquidation Distribution with respect to each Series of the Trust Preferred Securities, to the extent that the Issuer Trust shall have funds on hand available therefor at such time and (b) the amount of assets of the Issuer Trust remaining available for distribution to Holders of the Trust Preferred Securities on liquidation of the Issuer Trust.

“ Guarantee Trustee ” means The Bank of New York Mellon Trust Company, National Association, solely in its capacity as Guarantee Trustee and not in its individual capacity, until a Successor Guarantee Trustee has been appointed and has accepted such appointment pursuant to the terms of this Guarantee Agreement, and thereafter means each such Successor Guarantee Trustee.

“ Guarantor ” has the meaning specified in the first paragraph of this Guarantee Agreement.

“ Holder ” means any Holder of any Trust Preferred Securities; provided , however , that in determining whether the holders of the requisite percentage of Trust Preferred Securities of any Series have given any request, notice, consent or waiver hereunder, “Holder” shall not include the Guarantor, the Guarantee Trustee, or any Affiliate of the Guarantor or the Guarantee Trustee.

“ Issuer Trust ” has the meaning specified in the first paragraph of this Guarantee Agreement.

“ List of Holders ” has the meaning specified in Section 2.2(a).

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“ Officers’ Certificate ” means, with respect to any Person, a certificate signed by the Chairman of the Board, a Vice Chairman of the Board, the President or a Vice President, and by the Treasurer, an Assistant Treasurer, the Controller, an Assistant Controller, the Secretary or an Assistant Secretary, of such Person, and delivered to the Guarantee Trustee. One of the officers signing an Officer’s Certificate given pursuant to Section 2.5 shall be the principal executive, financial or accounting officer of the Guarantor. Any Officers’ Certificate delivered with respect to compliance with a condition or covenant provided for in this Guarantee Agreement shall include:

(i) a statement that each officer signing the Officers’ Certificate has read the covenant or condition and the definitions relating thereto;

(ii) a brief statement of the nature and scope of the examination or investigation undertaken by each such officer in rendering the Officers’ Certificate;

(iii) a statement that each officer has made such examination or investigation as, in such officer’s opinion, is necessary to enable such officer to express an informed opinion as to whether or not such covenant or condition has been complied with; and

(iv) a statement as to whether, in the opinion of each officer, such condition or covenant has been complied with.

“ Responsible Officer ” means, with respect to the Guarantee Trustee, any officer within the corporate trust department of the Guarantee Trustee having direct responsibility for the administration of this Guarantee Agreement or to whom any corporate trust matter is referred because of such person’s knowledge of and familiarity with the particular subject.

“ Senior Debt ” has the meaning specified in the Indenture.

“ Stock Purchase Date ” has the meaning specified in the Stock Purchase Contract Agreement, dated as of the date hereof, between the Guarantor and the Issuer Trust (acting through the Property Trustee).

“ Successor Guarantee Trustee ” means a successor Guarantee Trustee possessing the qualifications to act as Guarantee Trustee under Section 4.1.

“ Trust Agreement ” means the Amended and Restated Trust Agreement of the Issuer Trust referred to in the recitals to this Guarantee Agreement, as modified, amended or supplemented from time to time.

“ Trust Indenture Act ” means the Trust Indenture Act of 1939, as amended.

ARTICLE II

Trust Indenture Act

Section 2.1 Trust Indenture Act; Application.

(a) This Guarantee Agreement is subject to the provisions of the Trust Indenture Act that are required to be part of this Guarantee Agreement and shall, to the extent applicable, be governed by such provisions.

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(b) If and to the extent that any provision of this Guarantee Agreement limits, qualifies or conflicts with the duties imposed by Sections 310 to 317, inclusive, of the Trust Indenture Act, such imposed duties shall control.

Section 2.2 List of Holders.

(a) The Guarantor will furnish or cause to be furnished to the Guarantee Trustee: (i) semi-annually, not more than 15 days after May 1 and November 1 in each year, a list, in such form as the Guarantee Trustee may reasonably require, of the names and addresses of the Holders as of such May 1 and November 1, and (ii) at such other times as the Guarantee Trustee may request in writing, within 30 days after the receipt by the Guarantor of any such request, a list of similar form and content as of a date not more than 15 days prior to the time such list is furnished, excluding from any such list names and addresses received by the Guarantee Trustee in its capacity as Securities Registrar.

(b) The Guarantee Trustee shall comply with its obligations under Section 311(a), Section 311(b) and Section 312(b) of the Trust Indenture Act.

Section 2.3 Reports by the Guarantee Trustee.

Within 60 days after May 15 of each year, commencing May 15, 2009, the Guarantee Trustee shall provide to the Holders such reports as are required by Section 313 of the Trust Indenture Act, if any, in the form and in the manner provided by Section 313 of the Trust Indenture Act. The Guarantee Trustee shall also comply with the requirements of Section 313(d) of the Trust Indenture Act.

Section 2.4 Periodic Reports to the Guarantee Trustee.

The Guarantor shall provide to the Guarantee Trustee, the Commission and the Holders such documents reports and information, if any, as required by Section 314 of the Trust Indenture Act and the compliance certificate required by Section 314 of the Trust Indenture Act, in the form, in the manner and at the times required by Section 314 of the Trust Indenture Act. Delivery of such reports, information and documents to the Guarantee Trustee is for informational purposes only and the Guarantee Trustee’s receipt of such shall not constitute constructive notice of any information contained therein or determinable from information contained therein, including the Guarantor’s compliance with any of its covenants hereunder (as to which the Guarantee Trustee is entitled to rely exclusively on Officers’ Certificates).

Section 2.5 Evidence of Compliance with Conditions Precedent.

The Guarantor shall provide to the Guarantee Trustee such evidence of compliance with such conditions precedent, if any, provided for in this Guarantee Agreement that relate to any of the matters set forth in Section 314(c) of the Trust Indenture Act. Any certificate or opinion required to be given by an officer of the Guarantor pursuant to Section 314(c)(1) may be given in the form of an Officers’ Certificate.

Section 2.6 Events of Default; Waiver.

The Holders of a Majority in Liquidation Amount of the Trust Preferred Securities may, by vote, on behalf of the Holders of all the Trust Preferred Securities, waive any past default or Event of Default and its consequences; provided that each Series of Trust Preferred Securities shall be entitled, in the case of any default or Event of Default that affects such Series differently from the other Series, to vote separately as a Series with respect thereto. Upon such waiver, any such default or Event of Default shall cease to exist, and any default or Event of Default arising therefrom shall be deemed to have been cured, for every purpose of this Guarantee Agreement, but no such waiver shall extend to any subsequent or other default or Event of Default or impair any right consequent therefrom.

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Section 2.7 Events of Default; Notice.

(a) The Guarantee Trustee shall, within 90 days after the occurrence of an Event of Default, transmit by mail, first class postage prepaid, to the Holders, notice of any such Event of Default actually known to a Responsible Officer of the Guarantee Trustee, unless such defaults have been cured before the giving of such notice; provided that, except in the case of a default in the payment of a Guarantee Payment, the Guarantee Trustee shall be protected in withholding such notice if and so long as a committee of Responsible Officers of the Guarantee Trustee in good faith determines that the withholding of such notice is in the interests of the Holders.

(b) The Guarantee Trustee shall not be deemed to have knowledge of any Event of Default unless a Responsible Officer charged with the administration of this Guarantee Agreement shall have obtained written notice of such Event of Default.

Section 2.8 Conflicting Interests.

The Trust Agreement and the Indenture shall be deemed to be specifically described in this Guarantee Agreement for the purposes of clause (i) of the first proviso contained in Section 310(b) of the Trust Indenture Act.

ARTICLE III

Powers, Duties and Rights of the Guarantee Trustee

Section 3.1 Powers and Duties of the Guarantee Trustee.

(a) This Guarantee Agreement shall be held by the Guarantee Trustee for the benefit of the Holders, and the Guarantee Trustee shall not transfer this Guarantee Agreement to any Person except a Holder exercising his or her rights pursuant to Section 5.4(iv) or to a Successor Guarantee Trustee on acceptance by such Successor Guarantee Trustee of its appointment to act as Successor Guarantee Trustee. The right, title and interest of the Guarantee Trustee shall automatically vest in any Successor Guarantee Trustee, upon acceptance by such Successor Guarantee Trustee of its appointment hereunder, and such vesting and cessation of title shall be effective whether or not conveyancing documents have been executed and delivered pursuant to the appointment of such Successor Guarantee Trustee.

(b) If an Event of Default has occurred and is continuing, the Guarantee Trustee shall enforce this Guarantee Agreement for the benefit of the Holders.

(c) The Guarantee Trustee, before the occurrence of any Event of Default and after the curing of all Events of Default that may have occurred, shall undertake to perform only such duties as are specifically set forth in this Guarantee Agreement, and no implied covenants shall be read into this Guarantee Agreement against the Guarantee Trustee. In case an Event of Default has occurred (that has not been cured or waived pursuant to Section 2.6), the Guarantee Trustee shall exercise such of the rights and powers vested in it by this Guarantee Agreement, and use the same degree of care and skill in its exercise thereof, as a prudent person would exercise or use under the circumstances in the conduct of his or her own affairs.

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(d) No provision of this Guarantee Agreement shall be construed to relieve the Guarantee Trustee from liability for its