Exhibit 99.3
The Bank of New York
101 Barclay Street, 21 West
New York, New York 10005
Attention:  Corporate Trust
             Trustee Administration

Ladies and Gentlemen:

      OnBank Capital Trust I, a trust formed under the laws of the State of
Delaware (the "Trust") proposes to make an offer (the "Exchange Offer") to
exchange its 9.25% Series A Capital Securities (Liquidation Amount $1,000 per
Capital Security) (the "Original Capital Securities") for its 9.25% Series B
Capital Securities (Liquidation Amount $1,000 per Capital Security) (the
"Exchange Capital Securities"). All of the beneficial interests represented by
common securities of the Trust are owned by ONBANCorp, Inc., a Delaware
corporation (the "Company"). The terms and conditions of the Exchange Offer as
currently contemplated are set forth in a prospectus, dated ______, 1997 (the
"Prospectus"), to be distributed to all record holders of the Original Capital
Securities. The Original Capital Securities and the Exchange Capital Securities
are collectively referred to herein as the "Securities."

      The Trust hereby appoints The Bank of New York to act as exchange agent
(the "Exchange Agent") in connection with the Exchange Offer. References
hereinafter to "you" shall refer to The Bank of New York.

      The Exchange Offer is expected to be commenced by the Trust on or about
__________, 1997. The Letter of Transmittal accompanying the Prospectus (or in
the case of book entry securities, the ATOP system) is to be used by the holders
of the Original Capital Securities to accept the Exchange Offer and contains
instructions with respect to (i) the delivery of certificates for Original
Capital Securities tendered in connection therewith and (ii) the book-entry
transfer of Securities to the Exchange Agent's account.

      The Exchange Offer shall expire at 5:00 P.M., New York City time, on
________, 1997 or on such later date or time to which the Trust may extend the
Exchange Offer (the "Expiration Date"). Subject to the terms and conditions set
forth in the Prospectus, the Trust expressly reserves the right to extend the
Exchange Offer from time to time by giving oral (to be confirmed in writing) or
written notice to you before 9:00 A.M., New York City time, on the business day
following the previously scheduled Expiration Date.

      The Trust expressly reserves the right to amend or terminate the Exchange
Offer, and not to accept for exchange any Original Capital Securities not
theretofore accepted for exchange, upon the occurrence of any of the conditions
of the Exchange Offer specified in the Prospectus under the caption "The
Exchange Offer--Conditions to


the Exchange Offer." The Trust will give oral (confirmed in writing) or written
notice of any amendment, termination or nonacceptance of Original Capital
Securities to you promptly after any amendment, termination or nonacceptance.

      In carrying out your duties as Exchange Agent, you are to act in
accordance with the following instructions:

      1. You will perform such duties and only such duties as are specifically
set forth in the section of the Prospectus captioned "The Exchange Offer" or as
specifically set forth herein; provided, however, that in no way will your
general duty to act in good faith be discharged by the foregoing.

      2. You will establish an account with respect to the Original Capital
Securities at The Depository Trust Company (the "Book-Entry Transfer Facility")
for purposes of the Exchange Offer within two business days after the date of
the Prospectus, and any financial institution that is a participant in the
Book-Entry Transfer Facility's system may make book-entry delivery of the
Original Capital Securities by causing the Book-Entry Transfer Facility to
transfer such Original Capital Securities into your account in accordance with
the Book-Entry Transfer Facility's procedure for such transfer.

      3. You are to examine each of the Letters of Transmittal and certificates
for Original Capital Securities (or confirmation of book-entry transfer into
your account at the Book-Entry Transfer Facility) and any other documents
delivered or mailed to you by or for holders of the Original Capital Securities
to ascertain whether: (i) the Letters of Transmittal and any such other
documents are duly executed and properly completed in accordance with
instructions set forth therein and (ii) the Original Capital Securities have
otherwise been properly tendered. In each case where the Letter of Transmittal
or any other document has been improperly completed or executed or any of the
certificates for Original Capital Securities are not in proper form for transfer
or some other irregularity in connection with the acceptance of the Exchange
Offer exists, you will endeavor to inform the presenters of the need for
fulfillment of all requirements and to take any other action as may be necessary
or advisable to cause such irregularity to be corrected.

      4. With the approval of any Administrative Trustee of the Trust or any
person designated in writing by the Company (a "Designated Officer") (such
approval, if given orally, to be confirmed in writing) or any other party
designated by any such Administrative Trustee or Designated Officer in writing,
you are authorized to waive any irregularities in connection with any tender of
Original Capital Securities pursuant to the Exchange Offer.

      5. Tenders of Original Capital Securities may be made only as set forth in
the Letter of Transmittal and in the section of the Prospectus captioned "The
Exchange Offer--Procedures for Tendering Original Capital Securities," and
Original Capital Securities shall be considered properly tendered to you only
when tendered in accordance with the procedures set forth therein.


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      Notwithstanding the provisions of this paragraph 5, Original Capital
Securities which any Administrative Trustee of the Trust or Designated Officer
of the Company shall approve as having been properly tendered shall be
considered to be properly tendered (such approval, if given orally, shall be
confirmed in writing).

      6. You shall advise the Trust and the Company with respect to any Original
Capital Securities received subsequent to the Expiration Date and accept their
instructions with respect to disposition of such Original Capital Securities.

      7. You shall accept tenders:

      (a) in cases where the Original Capital Securities are registered in two
or more names only if signed by all named holders;

      (b) in cases where the signing person (as indicated on the Letter of
Transmittal) is acting in a fiduciary or a representative capacity only when
proper evidence of such person's authority so to act is submitted; and

      (c) from persons other than the registered holder of Original Capital
Securities provided that customary transfer requirements, including any
applicable transfer taxes, are fulfilled.

      You shall accept partial tenders of Original Capital Securities where so
indicated and as permitted in the Letter of Transmittal and deliver certificates
for Original Capital Securities to the transfer agent for split-up and return
any untendered Original Capital Securities to the holder (or such other person
as may be designated in the Letter of Transmittal) as promptly as practicable
after expiration or termination of the Exchange Offer.

      8. Upon satisfaction or waiver of all of the conditions to the Exchange
Offer, the Trust will notify you (such notice if given orally, to be confirmed
in writing) of its acceptance, promptly after the Expiration Date, of all
Original Capital Securities properly tendered and you, on behalf of the Trust,
will exchange such Original Capital Securities for Exchange Capital Securities
and cause such Original Capital Securities to be canceled. Delivery of Exchange
Capital Securities will be made on behalf of the Trust by you at the rate of
$1,000 principal amount of Exchange Capital Securities for each $1,000 principal
amount of the corresponding series of Original Capital Securities tendered
promptly after notice (such notice if given orally, to be confirmed in writing)
of acceptance of said Original Capital Securities by the Trust; provided,
however, that in all cases, Original Capital Securities tendered pursuant to the
Exchange Offer will be exchanged only after timely receipt by you of
certificates for such Original Capital Securities (or confirmation of book-entry
transfer into your account at the Book-Entry Transfer Facility), a properly
completed and duly executed Letter of Transmittal (or facsimile thereof) with
any required signature guarantees and any other required documents. You shall
issue Exchange Capital Securities only in denominations of $1,000 or any
integral multiple thereof. Original Capital Securities may be tendered in whole
or in part in denominations of $100,000 and integral multiples of $1,000 in


                                        3


excess thereof, provided that if any Original Capital Securities are tendered
for exchange in part, the untendered principal amount thereof must be $100,000
or any integral multiple of $1,000 in excess thereof.

      9. Tenders pursuant to the Exchange Offer are irrevocable, except that,
subject to the terms and upon the conditions set forth in the Prospectus and the
Letter of Transmittal, Original Capital Securities tendered pursuant to the
Exchange Offer may be withdrawn at any time on or prior to the Expiration Date.

      10. The Trust shall not be required to exchange any Original Capital
Securities tendered if any of the conditions set forth in the Exchange Offer are
not met. Notice of any decision by the Trust not to exchange any Original
Capital Securities tendered shall be given orally (and confirmed in writing) or
in writing by the Trust to you.

      11. If, pursuant to the Exchange Offer, the Trust does not accept for
exchange all or part of the Original Capital Securities tendered because of an
invalid tender, the occurrence of certain other events set forth in the
Prospectus under the caption "The Exchange Offer--Conditions to the Exchange
Offer" or otherwise, you shall promptly after the expiration or termination of
the Exchange Offer return those certificates for unaccepted Original Capital
Securities (or effect appropriate book-entry transfer), together with any
related required documents and the Letters of Transmittal relating thereto that
are in your possession, to the persons who deposited them.

      12. All certificates for reissued Original Capital Securities, unaccepted
Original Capital Securities or for Exchange Capital Securities shall be
forwarded by (a) first-class certified mail, return receipt requested, under a
blanket surety bond protecting you and the Trust from loss or liability arising
out of the non-receipt or non-delivery of such certificates, (b) by registered
mail insured separately for the replacement value of each of such certificates,
or (c) by appropriate book-entry transfer.

      13. You are not authorized to pay or offer to pay any concessions,
commissions or solicitation fees to any broker, dealer, bank or other persons or
to engage or utilize any person to solicit tenders.

      14. As Exchange Agent hereunder you:

      (a) shall have no duties or obligations other than those specifically set
forth in the section of the Prospectus captioned "The Exchange Offer," the
Letter of Transmittal or herein or as may be subsequently agreed to in writing
by you and the Trust;

      (b) will be regarded as making no representations and having no
responsibilities as to the validity, sufficiency, value or genuineness of any of
the certificates or the Original Capital Securities represented thereby
deposited with you pursuant to the Exchange Offer, and will not be required to
and will make no representation as to the validity, value or genuineness of the
Exchange Offer;


                                        4


      (c) shall not be obligated to take any legal action hereunder which might
in your reasonable judgment involve any expense or liability, unless you shall
have been furnished with reasonable indemnity;

      (d) may reasonably rely on and shall be protected in acting in reliance
upon any certificate, instrument, opinion, notice, letter, telegram or other
document or security delivered to you and reasonably believed by you to be
genuine and to have been signed by the proper party or parties;

      (e) may reasonably act upon any tender, statement, request, agreement or
other instrument whatsoever not only as to its due execution and validity and
effectiveness of its provisions, but also as to the truth and accuracy of any
information contained therein, which you shall in good faith believe to be
genuine or to have been signed or represented by a proper person or persons;

      (f) may rely on and shall be protected in acting upon written or oral
instructions from any Administrative Trustee of the Trust or from any Designated
Officer of the Company;

      (g) may consult with your counsel with respect to any questions relating
to your duties and responsibilities and the advice or opinion of such counsel
shall be full and complete authorization and protection in respect of any action
taken, suffered or omitted to be taken by you hereunder in good faith and in
accordance with the advice or opinion of such counsel; and

      (h) shall not advise any person tendering Original Capital Securities
pursuant to the Exchange Offer as to the wisdom of making such tender or as to
the market value or decline or appreciation in market value of any Original
Capital Securities.

      15. You shall take such action as may from time to time be requested by
the Trust or its counsel or any Designated Officer of the Company (and such
other action as you may reasonably deem appropriate) to furnish copies of the
Prospectus, Letter of Transmittal and the Notice of Guaranteed Delivery (as
defined in the Prospectus) or such other forms as may be approved from time to
time by the Trust or the Company to all persons requesting such documents and to
accept and comply with telephone requests for information relating to the
Exchange Offer, provided that such information shall relate only to the
procedures for accepting (or withdrawing from) the Exchange Offer. The Trust
will furnish you with copies of such documents at your request. All other
requests for information relating to the Exchange Offer shall be directed to the
Trust, Attention: Douglas J. Mahoney.

      16. You shall advise by facsimile transmission or telephone, and promptly
thereafter confirm in writing to Douglas J. Mahoney of the Trust, and such other
person or persons as the Trust or the Company may request, daily (and more
frequently during the week immediately preceding the Expiration Date and if
otherwise requested) up to and including the Expiration Date, as to the number
of Original Capital Securities which have been tendered pursuant to the Exchange
Offer and the items received by


                                        5


you pursuant to this Agreement, separately reporting and giving cumulative
totals as to items properly received and items improperly received. In addition,
you will also inform, and cooperate in making available to, the Trust or the
Company or any such other person or persons upon oral request made from time to
time on or prior to the Expiration Date of such other information as it or such
person reasonably requests. Such cooperation shall include, without limitation,
the granting by you to the Trust or the Company and such person as the Trust or
the Company may request of access to those persons on your staff who are
responsible for receiving tenders, in order to ensure that immediately prior to
the Expiration Date the Trust or the Company shall have received information in
sufficient detail to enable it to decide whether to extend the Exchange Offer.
You shall prepare a final list of all persons whose tenders were accepted, the
aggregate principal amount of Original Capital Securities tendered, the
aggregate principal amount of Original Capital Securities accepted and deliver
said list to the Trust promptly after the Expiration Date.

      17. Any Letters of Transmittal and Notices of Guaranteed Delivery which
are received by the Exchange Agent shall be stamped by you as to the date and
the time of receipt thereof and shall be preserved by you for a period of time
at least equal to the period of time you preserve other records pertaining to
the transfer of securities. You shall dispose of unused Letters of Transmittal
and other surplus materials by returning them to the Trust at the address set
forth below for notices.

      18. You hereby expressly waive any lien, encumbrance or right of set-off
whatsoever that you may have with respect to funds deposited with you for the
payment of transfer taxes by reasons of amounts, if any, borrowed by the Trust,
or any of its subsidiaries or affiliates pursuant to any loan or credit
agreement with you or for compensation owed to you hereunder.

      19. For services rendered as Exchange Agent hereunder, you shall be
entitled to such compensation as set forth on Schedule I attached hereto.

      20. You hereby acknowledge receipt of the Prospectus and the Letter of
Transmittal and further acknowledge that you have examined each of them. Any
inconsistency between this Agreement, on the one hand, and the Prospectus and
the Letter of Transmittal (as they may be amended from time to time), on the
other hand, shall be resolved in favor of the latter two documents, except with
respect to the duties, liabilities and indemnification of you as Exchange Agent,
which shall be controlled by this Agreement.

      21. (a) The Trust covenants and agrees to indemnify and hold you harmless
in your capacity as Exchange Agent hereunder against any loss, liability, cost
or expense, including reasonable attorneys' fees and expenses, arising out of or
in connection with any act, omission, delay or refusal made by you in reliance
upon any signature, endorsement, assignment, certificate, order, request,
notice, instruction or other instrument or document reasonably believed by you
to be valid, genuine and sufficient and in accepting any tender or effecting any
transfer of Original Capital Securities reasonably believed by you in good faith
to be authorized, and in delaying or refusing in


                                        6


good faith to accept any tenders or effect any transfer of Original Capital
Securities; provided, however, that the Trust shall not be liable for
indemnification or otherwise for any loss, liability, cost or expense to the
extent arising out of your gross negligence or willful misconduct. In no case
shall the Trust be liable under this indemnity with respect to any claim against
you unless the Trust shall be notified by you, by letter or cable or by
facsimile confirmed by letter, of the written assertion of a claim against you
or of any other action commenced against you, promptly after you shall have
received any such written assertion or notice of commencement of action. The
Trust shall be entitled to participate at its own expense in the defense of any
such claim or other action, and, if the Trust so elects, the Trust may assume
the defense of any suit brought to enforce any such claim. In the event that the
Trust shall assume the defense of any such suit or threatened action in respect
of which indemnification may be sought hereunder, the Trust shall not be liable
for the fees and expenses of any additional counsel thereafter retained by you
so long as you consent to the Trust's retention of counsel, which consent may
not be unreasonably withheld; provided that the Trust shall not be entitled to
assume the defense of any such action if the named parties to such action
include both the Trust and you and representation of both parties by the same
legal counsel would, in the written opinion of counsel to you, be inappropriate
due to actual or potential conflicting interests between you and the Trust. It
is understood that the Trust shall not be liable under this paragraph for the
fees and expenses of more than one legal counsel for you. In the event that the
Trust shall assume the defense of any such suit, the Trust shall not thereafter
be liable for the fees and expenses of any counsel retained by you.

      (b) You agree that, without the prior written consent of the Trust (which
consent shall not be unreasonably withheld), you will not settle, compromise or
consent to the entry of any pending or threatened claim, action or proceeding in
respect of which indemnification could be sought in accordance with the
indemnification provisions of this Agreement (whether or not you or the Trust or
any of its trustees, or controlling persons is an actual or potential party to
such claim, action or proceeding), unless such settlement, compromise or consent
includes an unconditional release of the Trust and its trustees and controlling
persons from all liability arising out of such claim, action or proceeding.

      22. You shall arrange to comply with all requirements under the tax laws
of the United States, including those relating to missing Tax Identification
Numbers, and shall file any appropriate reports with the Internal Revenue
Service. The Trust understands that you are required in certain instances to
deduct 31% with respect to interest paid on the Exchange Capital Securities and
proceeds from the sale, exchange, redemption or retirement of the Exchange
Capital Securities from holders who have not supplied their correct Taxpayer
Identification Number or required certification. Such funds will be turned over
to the Internal Revenue Service in accordance with applicable regulations.

      23. You shall notify the Trust of the amount of any transfer taxes payable
in respect of the exchange of Original Capital Securities and, upon receipt of
written approval from the Trust, you shall deliver or cause to be delivered, in
a timely manner


                                        7


to each governmental authority to which any transfer taxes are payable in
respect of the exchange of Original Capital Securities, your check in the amount
of all transfer taxes so payable, and the Trust shall reimburse you for the
amount of any and all transfer taxes payable in respect of the exchange of
Original Capital Securities; provided, however, that you shall reimburse the
Trust for amounts refunded to you in respect of your payment of any such
transfer taxes, at such time as such refund is received by you.

      24. This Agreement and your appointment as Exchange Agent hereunder shall
be construed and enforced in accordance with the laws of the State of New York
applicable to agreements made and to be performed entirely within such state,
and without regard to conflicts of law principles, and shall inure to the
benefit of, and the obligations created hereby shall be binding upon, the
successors and assigns of each of the parties hereto.

      25. This Agreement may be executed in one or more counterparts, each of
which shall be deemed to be an original and all of which taken together shall
constitute one and the same agreement.

      26. In case any provision of this Agreement 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.

      27. This Agreement shall not be deemed or construed to be modified,
amended, rescinded, canceled or waived, in whole or in part, except by a written
instrument signed by a duly authorized representative of the party to be
charged. This Agreement may not be modified orally.

      28. Unless otherwise provided herein, all notices, requests and other
communications to any party hereunder shall be in writing (including facsimile
or similar writing) and shall be given to such party, addressed to it, at its
address or telecopy number set forth below:

      If to the Trust:
            OnBank Capital Trust I
            101 South Salina Street
            P. O. Box 4983
            Syracuse, NY  13221-4983

            Facsimile:  (315) _______
            Attention:   William M. LeBean
                         Administrative Trustee


                                        8


      If to the Exchange Agent:

            The Bank of New York
            101 Barclay Street, 21 West
            New York, NY  10283
            Telephone:  (212) ________
            Facsimile:  (212) ________
            Attention:  Corporate Trust
                          Trustee Administration

      29. Unless terminated earlier by the parties hereto, this Agreement shall
terminate 90 days following the Expiration Date. Notwithstanding the foregoing,
Paragraphs 19, 21 and 23 shall survive the termination of this Agreement. Upon
any termination of this Agreement, you shall promptly deliver to the Trust any
certificates for Securities, funds or property then held by you as Exchange
Agent under this Agreement.

      30. This Agreement shall be binding and effective as of the date hereof.

      Please acknowledge receipt of this Agreement and confirm the arrangements
herein provided by signing and returning the enclosed copy.


     ONBANK CAPITAL TRUST I


     By: 
         ----------------------------------
          Name:
          Title:    Administrative Trustee


Accepted as the date first above written:


THE BANK OF NEW YORK, as Exchange Agent


By:
    ---------------------------
     Name:
     Title:


                                        9


                              THE BANK OF NEW YORK
                                  FEE SCHEDULE
                            EXCHANGE AGENTS SERVICES
                             ONBANK CAPITAL TRUST I

I.    Exchange Agency

      A fee for the receipt of exchanged 9.25% Capital Securities of OnBank
      Capital Trust I will be charged at $____ per letter of transmittal. The
      total charge will be subject to a minimum of $____ and maximum of $_____.

      This fee covers examination and execution of all required documentation,
      receipt of transmittal letters, reporting as required to the Company and
      communication with DTC.

II.   Miscellaneous

      Fees for services not specifically covered in this schedule will be
      assessed in amounts commensurate with the services rendered.


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