GUARANTEE AGREEMENT Between S&T BANCORP, INC. (as Guarantor) and [ ]

Exhibit (4)(p)

GUARANTEE AGREEMENT

Between

S&T BANCORP, INC.

(as Guarantor)

and

[    ]

(as Guarantee Trustee)

dated as of

[      ], [    ]

S&T CAPITAL TRUST [I] [II] [III]

Certain Sections of this Guarantee Agreement relating to

Sections 310 through 318 of the

Trust Indenture Act of 1939:

Note: This reconciliation and tie shall not, for any purpose, be deemed to be a part of the Guarantee Agreement.

TABLE OF CONTENTS

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GUARANTEE AGREEMENT

This GUARANTEE AGREEMENT, dated as of [        ], [        ] is executed and delivered by S&T BANCORP, INC., a Pennsylvania corporation (the “Guarantor” ), having its principal office at 800 Philadelphia Street, Indiana, Pennsylvania 15701 and [        ], a [        ] banking corporation, as trustee (the “Guarantee Trustee” ), for the benefit of the Holders (as defined herein) from time to time of the Capital Securities (as defined herein) of S&T Capital Trust [I] [II] [III], a Delaware statutory trust (the “Issuer Trust” ).

WHEREAS, pursuant to an Amended and Restated Trust Agreement (the “Trust Agreement” ), dated as of [            ], [            ], among the Guarantor, as Depositor, [            ], as Property Trustee (the “Property Trustee” ), [            ], as Delaware Trustee (the “Delaware Trustee” ) (collectively, the “Issuer Trustees” ) and the Holders from time to time of preferred undivided beneficial interests in the assets of the Issuer Trust, the Issuer Trust is issuing $[            ] aggregate Liquidation Amount (as defined herein) of its Capital Securities, Liquidation Amount $[            ] per preferred security (the “Capital Securities” ), representing preferred undivided beneficial interests in the assets of the Issuer Trust and having the terms set forth in the Trust Agreement;

WHEREAS, the Capital Securities will be issued by the Issuer Trust and the proceeds thereof, together with the proceeds from the issuance of the Issuer Trust’s Common Securities (as defined herein), will be used to purchase the Junior Subordinated Debentures due [        ], [        ] (as defined in the Trust Agreement) (the “Junior Subordinated Debentures” ) of the Guarantor which will be deposited with [        ], as Property Trustee under the Trust Agreement, as trust assets; and

WHEREAS, as incentive for the Holders to purchase Capital Securities, the Guarantor desires irrevocably and unconditionally to agree, to the extent set forth herein, to pay to the Holders of the Capital 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 Capital Securities by each Holder, which purchase the Guarantor hereby acknowledges shall benefit the Guarantor, and intending to be legally bound hereby, the Guarantor executes and delivers this Guarantee Agreement for the benefit of the Holders from time to time of the Capital Securities.

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 terms used but not otherwise defined herein shall have the meanings assigned to such terms in the Trust Agreement or, if not defined therein, in the Indenture as in effect on the date hereof.

“Additional Amount” has the meaning specified in the Trust Agreement.

“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. 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.

“Capital Securities” shall have the meaning specified in the first recital of this Guarantee Agreement.

“Common Securities” means the securities representing common undivided beneficial interests in the assets of the Issuer Trust.

“Delaware Trustee” shall have the meaning specified in the first recital of this Guarantee Agreement.

“Distributions” means preferential cumulative cash distributions accumulating from [            ], [        ] and payable [monthly] [quarterly] [semi-annually] in arrears on [        ], [        ], [        ], and [        ] of each year, commencing [        ], [    ] at the annual rate of [    ]% of the Liquidation Amount.

“Event of Default” means (a) a default by the Guarantor in any of its payment obligations under this Guarantee Agreement, or (b) a default by the Guarantor in any other obligation hereunder that remains unremedied for 30 days.

“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 Capital Securities, to the extent not paid or made by or on behalf of the Issuer Trust: (a) any accumulated and unpaid Distributions (as defined in the Trust Agreement) required to be paid on the Capital Securities, to the extent the Issuer Trust shall have funds on hand available therefor at such time, (b) the Redemption Price, with respect to the Capital Securities called for redemption by the Issuer Trust to the extent that the Issuer Trust shall have funds on hand available therefor at such time, and (c) upon a voluntary or involuntary termination, winding-up or liquidation of the Issuer Trust, unless Junior Subordinated Debentures are distributed to the Holders, the lesser of (i) the Liquidation Amount and all accumulated and unpaid Distributions to the date of payment to the extent the Issuer Trust shall have funds on hand available to make such payment at such time and (ii) the amount of assets of the Issuer Trust remaining available for distribution to Holders in liquidation of the Issuer Trust (in either case, the “Liquidation Distribution” ).

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“Guarantee Trustee” means [    ], 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” shall have the meaning specified in the first paragraph of this Guarantee Agreement.

“Holder” means any holder, as registered on the books and records of the Issuer Trust, of any Capital Securities; provided, however , that, in determining whether the holders of the requisite percentage of Capital Securities 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.

“Indenture” means the Junior Subordinated Indenture dated as of [    ], [    ], between S&T Bancorp, Inc. and [            ], as trustee, as may be modified, amended or supplemented from time to time.

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

“Issuer Trustees” shall have the meaning specified in the first recital of this Guarantee Agreement.

“Junior Subordinated Debentures ” shall have the meaning specified in the first recital of this Guarantee Agreement.

“Like Amount” means (a) with respect to a redemption of Capital Securities, Capital Securities having a Liquidation Amount equal to the principal amount of Junior Subordinated Debentures to be contemporaneously redeemed in accordance with the Indenture, the proceeds of which will be used to pay the Redemption Price of such Capital Securities, (b) with respect to a distribution of Junior Subordinated Debentures to Holders of Capital Securities in connection with a dissolution or liquidation of the Issuer Trust, Junior Subordinated Debentures having a principal amount equal to the Liquidation Amount of the Capital Securities of the Holder to whom such Junior Subordinated Debentures are distributed, and (c) with respect to any distribution of an Additional Amount to Holders of Capital Securities, Junior Subordinated Debentures having a principal amount equal to the Liquidation Amount of the Capital Securities in respect of which such distribution is made.

“Liquidation Amount” means the stated amount of $[        ] per Capital Security.

“Majority in Liquidation Amount of the Capital Securities” means, except as provided by the Trust Indenture Act, Capital Securities representing more than 50% of the aggregate Liquidation Amount of all then outstanding Capital Securities issued by the Issuer Trust.

“Officers’ Certificate” means, with respect to any Person, a certificate signed by the Chairman of the Board, Chief Executive Officer, President or a Vice President, and by the Chief

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Financial Officer, Treasurer or Secretary of such Person, and delivered to the Guarantee Trustee. Any Officers’ Certificate delivered with respect to compliance with a condition or covenant provided for in this Guarantee Agreement shall include:

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

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

(c) a statement that such 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

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

“Person” means a legal person, including any individual, corporation, estate, partnership, joint venture, association, joint stock company, limited liability company, trust, unincorporated association, or government or any agency or political subdivision thereof, or any other entity of whatever nature.

“Property Trustee” shall have the meaning specified in the first recital of this Guarantee Agreement.

“Redemption Date” means, with respect to any Capital Security to be redeemed, the date fixed for such redemption by or pursuant to the Trust Agreement; provided that each Junior Subordinated Debenture Redemption Date (as such term is defined in the Indenture) and the stated maturity of the Junior Subordinated Debentures shall be a Redemption Date for a Like Amount of Capital Securities.

“Redemption Price” shall have the meaning specified in the Trust Agreement.

“Responsible Officer” means, when used with respect to the Guarantee Trustee, any officer assigned to the Corporate Trust Office, including any managing director, principal, vice president, assistant vice president, assistant treasurer, assistant secretary or any other officer of the Guarantee Trustee customarily performing functions similar to those performed by any of the above designated officers, and having direct responsibility for the administration of this Guarantee Agreement, and also, with respect to a particular matter, any other officer to whom such matter is referred because of such officer’s knowledge of and familiarity with the particular subject.

“Senior Indebtedness” shall have the meaning specified in the Indenture.

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

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“Trust Agreement” means the Amended and Restated Trust Agreement, dated [            ], [    ], executed by S&T Bancorp, Inc., as Depositor, [            ], as Delaware Trustee, and [            ], as Property Trustee and subscribed to and accepted by the Administors.

“Trust Indenture Act” means the Trust Indenture Act of 1939, as amended by the Trust Indenture Reform Act of 1990, or any successor statute, in each case as amended from time to time.

ARTICLE II

TRUST INDENTURE ACT

Section 2.1. Trust Indenture Act; Application.

If any provision hereof limits, qualifies or conflicts with a provision of the Trust Indenture Act that is required under such Act to be a part of and govern this Guarantee Agreement, the provision of the Trust Indenture Act shall control. If any provision of this Guarantee Agreement modifies or excludes any provision of the Trust Indenture Act that may be so modified or excluded, the latter provision shall be deemed to apply to this Guarantee Agreement as so modified or excluded, as the case may be.

Section 2.2. List of Holders.

(a) In the event that the Guarantee Trustee is not also acting as the Securities Registrar, the Guarantor will furnish or cause to be furnished to the Guarantee Trustee:

(i) not less than one day nor more than 15 days prior to every Interest Payment Date, a list, in such form as the Guarantee Trustee may reasonably require, of the names and addresses of the Holders as of such date; 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.

(b) The Guarantee Trustee shall comply with the requirements of Section 312(b) of the Trust Indenture Act.

Section 2.3. Reports by the Guarantee Trustee.

Within 60 days of January 31 of each year commencing January 31, [        ], the Guarantee Trustee shall provide to the Holders such reports, if any, as are required by Section 313 of the Trust Indenture Act 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.

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Section 2.4. Periodic Reports to the Guarantee Trustee.

The Guarantor shall provide to the Guarantee Trustee 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.

Section 2.5. Evidence of Compliance with Conditions Precedent.

The Guarantor shall pr