Exhibit 99.1


                     THE TRANSFER OF THIS AGREEMENT IS SUBJECT TO
                      CERTAIN PROVISIONS CONTAINED HEREIN AND TO
                            RESALE RESTRICTIONS UNDER THE
                          SECURITIES ACT OF 1933, AS AMENDED


         STOCK OPTION AGREEMENT, dated October 28, 1997, between ONBANCorp,
Inc., a Delaware corporation ("Issuer"), and First Empire State Corporation, a
New York corporation ("Grantee").

                                 W I T N E S S E T H:

         WHEREAS, Grantee, Issuer and Olympia Financial Corp., a Delaware
corporation and a wholly owned subsidiary of Grantee ("Merger Sub") have entered
into an Agreement and Plan of Reorganization of even date herewith (the
"Reorganization Agreement"), which agreement has been executed by the parties
hereto immediately prior to this Stock Option Agreement (the "Agreement"), and
will enter into an Agreement and Plan of Merger to be dated as of the date of
this Agreement (the "Plan of Merger," and, together with the Reorganization
Agreement, the "Merger Agreements"); and

         WHEREAS, as a condition to Grantee's entering into the Merger
Agreements and in consideration therefor, Issuer has agreed to grant Grantee the
Option (as hereinafter defined);

         NOW, THEREFORE, in consideration of the foregoing and the mutual
covenants and agreements set forth herein and in the Merger Agreements, the
parties hereto agree as follows:

         1.(a)  Issuer hereby grants to Grantee an unconditional, irrevocable
option (the "Option") to purchase, subject to the terms hereof, up to 2,529,000
fully paid and nonassessable shares of Issuer's Common Stock, par value $1.00
per share ("Common Stock"), at a price of $60.00 per share (the "Option Price");
provided, however, that in no event shall the number of shares of Common Stock
for which this Option is exercisable exceed 19.9% of the Issuer's issued and
outstanding shares of Common Stock without giving effect to any shares subject
to or issued pursuant to the Option.  The number of shares of Common Stock that
may be received upon the exercise of the Option and the Option Price are subject
to adjustment as herein set forth.

         (b) In the event that any additional shares of Common Stock are either
(i) issued or otherwise become out-



standing after the date of this Agreement (other than pursuant to this Agreement
or as permitted under the terms of the Merger Agreements) or (ii) redeemed,
repurchased, retired or otherwise cease to be outstanding after the date of the
Agreement, the number of shares of Common Stock subject to the Option shall be
increased or decreased, as appropriate, so that, after such issuance, such
number equals 19.9% of the number of shares of Common Stock then issued and
outstanding without giving effect to any shares subject or issued pursuant to
the Option.  Nothing contained in this Section 1(b) or elsewhere in this
Agreement shall be deemed to authorize Issuer or Grantee to breach any provision
of the Merger Agreements.

         2.(a)  The Holder (as hereinafter defined) may exercise the Option, in
whole or part, and from time to time, if, but only if, both an Initial
Triggering Event (as hereinafter defined) and a Subsequent Triggering Event (as
hereinafter defined) shall have occurred prior to the occurrence of an Exercise
Termination Event (as hereinafter defined), provided, however, that the Holder
shall have sent the written notice of such exercise (as provided in subsection
(e) of this Section 2) within six months following such Subsequent Triggering
Event, provided further, however, that if the Option cannot be exercised on any
day because of any injunction, order or similar restraint issued by a court of
competent jurisdiction, the period during which the Option may be exercised
shall be extended so that the Option shall expire no earlier than on the 10th
business day after such injunction, order or restraint shall have been dissolved
or when such injunction, order or restraint shall have become permanent and no
longer subject to appeal, as the case may be.  Each of the following shall be an
"Exercise Termination Event":  (i) the Effective Time (as defined in the Plan of
Merger) of the Merger; (ii) termination of the Merger Agreements in accordance
with the provisions thereof if such termination occurs prior to the occurrence
of an Initial Triggering Event except a termination by Grantee pursuant to
Section 6.1(b)(i) of the Reorganization Agreement (unless the breach by Issuer
giving rise to such right of termination is non-volitional); or (iii) the
passage of 12 months after termination of the Merger Agreements if such
termination follows the occurrence of an Initial Triggering Event or is a
termination by Grantee pursuant to Section 6.1(b)(i) of the Reorganization
Agreement (unless the breach by Issuer giving rise to such right of termination
is non-volitional).  The term "Holder" shall mean the holder or holders of the
Option.  Notwithstanding anything to the contrary contained herein, the Option
may not be exercised (nor may Grantee's rights under Section 13 hereof be
exercised) at any time when Grantee shall be in willful breach of any of its
covenants or 

                                         2


agreements contained in the Merger Agreements under circumstances that would
entitle Issuer to terminate the Merger Agreements (without regard to any grace
period provided for in Section 6.1(b)(x) of the Reorganization Agreement).  In
the event that Issuer terminates the Merger Agreements under circumstances where
the proviso to Section 6.1(f) of the reorganization Agreement is applicable,
then immediately upon Grantee's receipt of the wire transfer contemplated by
such proviso to Section 6.1(f), this Agreement shall terminate and shall become
void and have no further force or effect and Grantee shall surrender this
Agreement to Issuer.

         (b) The term "Initial Triggering Event" shall mean any of the
following events or transactions occurring after the date hereof:

              (i)  Issuer or any of its Subsidiaries (each an "Issuer
    Subsidiary"), without having received Grantee's prior written consent,
    shall have entered into an agreement to engage in an Acquisition
    Transaction (as hereinafter defined) with any person (the term "person" for
    purposes of this Agreement having the meaning assigned thereto in 
    Sections 3(a)(9) and 13(d)(3) of the Securities Exchange Act of 1934, as 
    amended (the "1934 Act"), and the rules and regulations thereunder) other 
    than Grantee or any of its Subsidiaries (each a "Grantee Subsidiary") or 
    Issuer or any of its Subsidiaries, without having received Grantee's prior 
    written consent, shall have authorized, recommended, proposed, or publicly
    announced its intention to authorize, recommend or propose to engage in an
    Acquisition Transaction with any person other than Grantee or a Subsidiary
    of Grantee.  For purposes of this Agreement, "Acquisition Transaction"
    shall mean (w) a merger or consolidation, or any similar transaction,
    involving Issuer or any Significant Subsidiary (as defined in Rule 1-02 of
    Regulation S-X promulgated by the Securities and Exchange Commission (the
    "SEC")) of Issuer, (x) a purchase, lease or other acquisition or assumption
    of all or a substantial portion of the assets or deposits of Issuer or any
    Significant Subsidiary of Issuer, (y) a purchase or other acquisition
    (including by way of merger, consolidation, share exchange or otherwise) of
    securities representing 10% or more of the voting power of Issuer, or (z)
    any substantially similar transaction; provided, however, that in no event
    shall any merger, consolidation, purchase or similar transaction involving
    only the Issuer and one or more of its Subsidiaries or 

                                         3


    involving only two or more of such Subsidiaries, be deemed to be an
    Acquisition Transaction, provided that any such transaction is not entered
    into in violation of the terms of the Merger Agreements;
    
              (ii) Any person (other than Grantee or any Subsidiary of Grantee)
    shall have acquired beneficial ownership or the right to acquire beneficial
    ownership of 10% or more of the outstanding shares of Common Stock (the
    term "beneficial ownership" for purposes of this Agreement having the
    meaning assigned thereto in Section 13(d) of the 1934 Act, and the rules
    and regulations thereunder) or any person other than Grantee or any
    Subsidiary of Grantee shall have commenced (as such term is defined under
    the rules and regulations of the SEC), or shall have filed or publicly
    disseminated a registration statement or similar disclosure statement with
    respect to, a tender offer or exchange offer to purchase any shares of
    Issuer Common Stock such that, upon consummation of such offer, such person
    would own or control 10% or more of the then outstanding shares of Issuer
    Common Stock (such an offer being referred to herein as a "Tender Offer" or
    an "Exchange Offer," respectively);

              (iii)     (A)  the holders of Issuer Common Stock shall not have
    approved the Merger Agreements and the transactions contemplated thereby,
    at the meeting of such stockholders held for the purpose of voting on such
    agreement, (B) such meeting shall not have been held or shall have been
    cancelled prior to termination of the Merger Agreements, or (C) the Board
    of Directors of Issuer shall have publicly withdrawn or modified, or
    publicly announced its intent to withdraw or modify, in any manner adverse
    to Grantee, its recommendation that the stockholders of Issuer approve the
    transactions contemplated by the Merger Agreements, in each case after it
    shall have been publicly announced that any person other than Grantee or
    any Subsidiary of Grantee shall have (x) made, or disclosed an intention to
    make, a proposal to engage in an Acquisition Transaction, (u) commenced a
    Tender Offer, or filed or publicly disseminated a registration statement or
    similar disclosure statement with respect to an Exchange Offer, or (z)
    filed an application (or given a notice), whether in draft or final form,
    under any federal or state banking laws seeking regulatory approval to
    engage in an Acquisition Transaction; or
    
    

                                         4



              (iv) After an overture is made by a third party to Issuer or its
    stockholders to engage in an Acquisition Transaction, Issuer shall have
    breached any covenant or obligation contained in the Reorganization
    Agreement and such breach (x) would entitle Grantee to terminate the Merger
    Agreements and (y) shall not have been cured prior to the Notice Date (as
    defined below).

         (c)  The term "Subsequent Triggering Event" shall mean either of the
following events or transactions occurring after the date hereof:

              (i)  The acquisition by any person of beneficial ownership of 25%
    or more of the then outstanding shares of Common Stock; or
    
              (ii) The occurrence of the Initial Triggering Event described in
    paragraph (i) of subsection (b) of this Section 2, except that the
    percentage referred to in clause (y) shall be 25%.

         (d)  Issuer shall notify Grantee promptly in writing of the occurrence
of any Initial Triggering Event or Subsequent Triggering Event of which it has
notice (together, a "Triggering Event"), it being understood that the giving of
such notice by Issuer shall not be a condition to the right of the Holder to
exercise the Option.

         (e)  In the event the Holder is entitled to and wishes to exercise the
Option, it shall send to Issuer a written notice (the date of which being herein
referred to as the "Notice Date") specifying (i) the total number of shares it
will purchase pursuant to such exercise and (ii) a place and date not earlier
than three business days nor later than 60 business days from the Notice Date
for the closing of such purchase (the "Closing Date"); provided that if prior
notification to or approval of the Federal Reserve Board or any other regulatory
agency is required in connection with such purchase, the Holder shall promptly
file the required notice or application for approval and shall expeditiously
process the same and the period of time that otherwise would run pursuant to
this sentence shall run instead from the date on which any required notification
periods have expired or been terminated or such approvals have been obtained and
any requisite waiting period or periods shall have passed.  Any exercise of the
Option shall be deemed to occur on the Notice Date relating thereto.

                                         5



         (f)  At the closing referred to in subsection (e) of this Section 2,
the Holder shall pay to Issuer the aggregate purchase price for the shares of
Common Stock purchased pursuant to the exercise of the Option in immediately
available funds by wire transfer to a bank account designated by Issuer,
provided that failure or refusal of Issuer to designate such a bank account
shall not preclude the Holder from exercising the Option.

         (g)  At such closing, simultaneously with the delivery of immediately
available funds as provided in subsection (f) of this Section 2, Issuer shall
deliver to the Holder a certificate or certificates representing the number of
shares of Common Stock purchased by the Holder and, if the Option should be
exercised in part only, a new Option evidencing the rights of the Holder thereof
to purchase the balance of the shares purchasable hereunder, and the Holder
shall deliver to Issuer a copy of this Agreement and a letter agreeing that the
Holder will not offer to sell or otherwise dispose of such shares in violation
of applicable law or the provisions of this Agreement.

         (h)  Certificates for Common Stock delivered at a closing hereunder
may be endorsed with a restrictive legend that shall read substantially as
follows:

         "The transfer of the shares represented by this certificate is subject
         to certain provisions of an agreement between the registered holder
         hereof and Issuer and to resale restrictions arising under the 
         Securities Act of 1933, as amended.  A copy of such agreement is on
         file at the principal office of Issuer and will be provided to the
         holder hereof without charge upon receipt by Issuer of a written
         request therefor."

It is understood and agreed that:  (i) the reference to the resale restrictions
of the Securities Act of 1933, as amended (the "1933 Act"), in the above legend
shall be removed by delivery of substitute certificate(s) without such reference
if the Holder shall have delivered to Issuer a copy of a letter from the staff
of the SEC, or an opinion of counsel, in form and substance reasonably
satisfactory to Issuer, to the effect that such legend is not required for
purposes of the 1933 Act; (ii) the reference to the provisions to this Agreement
in the above legend shall be removed by delivery of substitute certificate(s)
without such reference if the shares have been sold or transferred in compliance
with the provisions of this Agreement and under circumstances that do not
require the retention of such reference; and (iii) the legend 

                                         6



shall be removed in its entirety if the conditions in the preceding clauses (i)
and (ii) are both satisfied.  In addition, such certificates shall bear any
other legend as may be required by law.

         (i)  Upon the giving by the Holder to Issuer of the written notice of
exercise of the Option provided for under subsection (e) of this Section 2 and
the tender of the applicable purchase price in immediately available funds, the
Holder shall be deemed to be the holder of record of the shares of Common Stock
issuable upon such exercise, notwithstanding that the stock transfer books of
Issuer shall then be closed or that certificates representing such shares of
Common Stock shall not then be actually delivered to the Holder.  Issuer shall
pay all expenses, and any and all United States federal, state and local taxes
and other charges that may be payable in connection with the preparation, issue
and delivery of stock certificates under this Section 2 in the name of the
Holder or its assignee, transferee or designee.

         3. Issuer agrees:  (i) that it shall at all times maintain, free from
preemptive rights, sufficient authorized but unissued or treasury shares of
Common Stock so that the Option may be exercised without additional
authorization of Common Stock after giving effect to all other options,
warrants, convertible securities and other rights to purchase Common Stock; (ii)
that it will not, by charter amendment or through reorganization, consolidation,
merger, dissolution or sale of assets, or by any other voluntary act, avoid or
seek to avoid the observance or performance of any of the covenants,
stipulations or conditions to be observed or performed hereunder by Issuer;
(iii) promptly to take all action as may from time to time be required
(including (x) complying with all premerger notification, reporting and waiting
period requirements specified in 15 U.S.C. Section 18a and regulations
promulgated thereunder and (y) in the event, under federal or state banking law,
prior approval of or notice to the Federal Reserve Board or any other federal or
state regulatory authority is necessary before the Option may be exercised,
cooperating fully with the Holder in preparing such applications or notices and
providing such information to the Federal Reserve Board or such other federal or
state regulatory authority as they may require) in order to permit the Holder to
exercise the Option and Issuer duly and effectively to issue shares of Common
Stock pursuant hereto; and (iv) promptly to take all action provided herein to
protect the rights of the Holder against dilution.

         4. This Agreement (and the Option granted hereby) are exchangeable,
without expense, at the option of the Hold-

                                         7


er, upon presentation and surrender of this Agreement at the principal office of
Issuer, for other Agreements providing for Options of different denominations
entitling the holder thereof to purchase, on the same terms and subject to the
same conditions as are set forth herein, in the aggregate the same number of
shares of Common Stock purchasable hereunder.  The terms "Agreement" and
"Option" as used herein include any Stock Option Agreements and related Options
for which this Agreement (and the Option granted hereby) may be exchanged.  Upon
receipt by Issuer of evidence reasonably satisfactory to it of the loss, theft,
destruction or mutilation of this Agreement, and (in the case of loss, theft or
destruction) of reasonably satisfactory indemnification, and upon surrender and
cancellation of this Agreement, if mutilated, Issuer will execute and deliver a
new Agreement of like tenor and date.  Any such new Agreement executed and
delivered shall constitute an additional contractual obligation on the part of
Issuer, whether or not the Agreement so lost, stolen, destroyed or mutilated
shall at any time be enforceable by anyone.

         5. In addition to the adjustment in the number of shares of Common
Stock that are purchasable upon exercise of the Option pursuant to Section 1 of
this Agreement, the number of shares of Common Stock purchasable upon the
exercise of the Option and the Option Price shall be subject to adjustment from
time to time as provided in this Section 5.  In the event of any change in, or
distributions in respect of, the Common Stock by reason of stock dividends,
split-ups,  mergers, recapitalizations, combinations, subdivisions, conversions,
exchanges of shares, distributions on or in respect of the Common Stock that
would be prohibited under the terms of the Merger Agreement, or the like, the
type and number of shares of Common Stock purchasable upon exercise hereof and
the Option Price shall be appropriately adjusted in such manner as shall fully
preserve the economic benefits provided hereunder and proper provision shall be
made in any agreement governing any such transaction to provide for such proper
adjustment and the full satisfaction of the Issuer's obligations hereunder.

         6. Upon the occurrence of a Subsequent Triggering Event that occurs
prior to an Exercise Termination Event, Issuer shall, at the request of Grantee
delivered within six months of such Subsequent Triggering Event (whether on its
own behalf or on behalf of any subsequent holder of this Option (or part
thereof) or any of the shares of Common Stock issued pursuant hereto), promptly
prepare, file and keep current a registration statement under the 1933 Act
covering this Option and any shares issued and issuable pursuant to this Option
and shall use its reasonable best efforts to 


                                         8


cause such registration statement to become effective and remain current in
order to permit the sale or other disposition of this Option and any shares of
Common Stock issued upon total or partial exercise of this Option ("Option
Shares") in accordance with any plan of disposition requested by Grantee. 
Issuer will use its reasonable best efforts to cause such registration statement
first to become effective and then to remain effective for such period not in
excess of 180 days from the day such registration statement first becomes
effective or such shorter time as may be reasonably necessary to effect such
sales or other dispositions.  Grantee shall have the right to demand two such
registrations.  The foregoing notwithstanding, if, at the time of any request by
Grantee for registration of the Option or Option Shares as provided above,
Issuer is in registration with respect to an underwritten public offering of
shares of Common Stock, and if in the good faith judgment of the managing
underwriter or managing underwriters, or, if none, the sole underwriter or
underwriters, of such offering the inclusion of the Holder's Option or Option
Shares would interfere with the successful marketing of the shares of Common
Stock offered by Issuer, the number of Option Shares otherwise to be covered in
the registration statement contemplated hereby may be reduced; and provided,
however, that after any such required reduction the number of Option Shares to
be included in such offering for the account of the Holder shall constitute at
least 25% of the total number of shares to be sold by the Holder and Issuer in
the aggregate; and provided further, however, that  if such reduction occurs,
then the Issuer shall file a registration statement for the balance as promptly
as practicable and no reduction shall thereafter occur.  Each such Holder shall
provide all information reasonably requested by Issuer for inclusion in any
registration statement to be filed hereunder.  If requested by any such Holder
in connection with such registration, Issuer shall become a party to any
underwriting agreement relating to the sale of such shares, but only to the
extent of obligating itself in respect of representations, warranties,
indemnities and other agreements customarily included in secondary offering
underwriting agreements for the Issuer.  Upon receiving any request under this
Section 6 from any Holder, Issuer agrees to send a copy thereof to any other
person known to Issuer to be entitled to registration rights under this Section
6, in each case by promptly mailing the same, postage prepaid, to the address of
record of the persons entitled to receive such copies.  Notwithstanding anything
to the contrary contained herein, in no event shall Issuer be obligated to
effect more than two registrations pursuant to this Section 6 by reason of the
fact that there shall be more 

                                         9



than one Grantee as a result of any assignment or division of this Agreement. 

         7. [reserved]

         8. [reserved]

         9. [reserved]

         10. The six-month period for exercise of certain rights under Sections
2, 6 and 13 shall be extended:  (i) to the extent necessary to obtain all
regulatory approvals for the exercise of such rights, and for the expiration of
all statutory waiting periods; and (ii) to the extent necessary to avoid
liability under Section 16(b) of the 1934 Act by reason of such exercise.

         11. Issuer hereby represents and warrants to Grantee as follows:

         (a) Issuer has full corporate power and authority to execute and
deliver this Agreement and to consummate the transactions contemplated hereby. 
The execution and delivery of this Agreement and the consummation of the
transactions contemplated hereby have been duly and validly authorized by the
Board of Directors of Issuer and no other corporate proceedings on the part of
Issuer are necessary to authorize this Agreement or to consummate the
transactions so contemplated.  This Agreement has been duly and validly executed
and delivered by Issuer. 

         (b) Issuer has taken all necessary corporate action to authorize and
reserve and to permit it to issue, and at all times from the date hereof through
the termination of this Agreement in accordance with its terms will have
reserved for issuance upon the exercise of the Option, that number of shares of
Common Stock equal to the maximum number of shares of Common Stock at any time
and from time to time issuable hereunder, and all such shares, upon issuance
pursuant hereto, will be duly authorized, validly issued, fully paid,
nonassessable, and will be delivered free and clear of all claims, liens,
encumbrance and security interests and not subject to any preemptive rights.

         12.  Grantee hereby represents and warrants to Issuer that:

         (a)  Grantee has all requisite corporate power and authority to enter
into this Agreement and, subject to any approvals or consents referred to
herein, to consummate the 


                                         10


transactions contemplated hereby.  The execution and delivery of this Agreement
and the consummation of the transactions contemplated hereby have been duly
authorized by all necessary corporate action on the part of Grantee.  This
Agreement has been duly executed and delivered by Grantee.

         (b)  The Option is not being, and any shares of Common Stock or other
securities acquired by Grantee upon exercise of the Option will not be, acquired
with a view to the public distribution thereof and will not be transferred or
otherwise disposed of except in a transaction registered or exempt from
registration under the Securities Act.

         13. Neither of the parties hereto may assign any of its rights or
obligations under this Agreement or the Option created hereunder to any other
person, without the express written consent of the other party, except that in
the event a Subsequent Triggering Event shall have occurred prior to an Exercise
Termination Event, Grantee, subject to the express provisions hereof, may assign
in whole or in part its rights and obligations hereunder within six months
following such Subsequent Triggering Event (or such later period as provided in
Section 10); provided, however, that until the date 15 days following the date
on which the Federal Reserve Board approves an application by Grantee to acquire
the shares of Common Stock subject to the Option, Grantee may not assign its
rights under the Option except in (i) a widely dispersed public distribution,
(ii) a private placement in which no one party acquires the right to purchase in
excess of 2% of the voting shares of Issuer, (iii) an assignment to a single
party (e.g., a broker or investment banker) for the purpose of conducting a
widely dispersed public distribution on Grantee's behalf, or (iv) any other
manner approved by the Federal Reserve Board.

         14. Each of Grantee and Issuer will use its best efforts to make all
filings with, and to obtain consents of, all third parties and governmental
authorities necessary to the consummation of the transactions contemplated by
this Agreement, including without limitation making application to list the
shares of Common Stock issuable hereunder on the Nasdaq National Market upon
official notice of issuance and applying to the Federal Reserve Board and the
OTS, as applicable, for approval to acquire the shares issuable hereunder, but
Grantee shall not be obligated to apply to state banking authorities for
approval to acquire the shares of Common Stock issuable hereunder until such
time, if ever, as it deems appropriate to do so.


                                         11


         15. (a)  Notwithstanding any other provision of this Agreement, in no
event shall the Grantee's Total Profit (as hereinafter defined) exceed $43.6
million and, if it otherwise would exceed such amount, the Grantee, at its sole
election, shall either (i) reduce the number of shares of Common Stock subject
to this Option, (ii) deliver to the Issuer for cancellation Option Shares
previously purchased by Grantee, (iii) pay cash to the Issuer, or (iv) any
combination thereof, so that Grantee's actually realized Total Profit shall not
exceed $43.6 million after taking into account the foregoing actions.

         (b)  Notwithstanding any other provision of this Agreement, this
Option may not be exercised for a number of shares as would, as of the date of
exercise, result in a Notional Total Profit (as defined below) of more than
$43.6 million; provided, that nothing in this sentence shall restrict any
exercise of the Option permitted hereby on any subsequent date.

         (c)  As used herein, the term "Total Profit" shall mean the aggregate
amount (before taxes) of (i)(x) the net cash amounts received by Grantee
pursuant to the sale of Option Shares (or any other securities into which such
Option Shares are converted or exchanged) to any unaffiliated party, less (y)
the Grantee's purchase price of such Option Shares, plus (ii) any amounts
received by Grantee on the transfer of the Option (or any portion thereof) to
any unaffiliated party.

         (d)  As used herein, the term "Notional Total Profit" with respect to
any number of shares as to which Grantee may propose to exercise this Option
shall be the Total Profit determined as of the date of such proposed exercise
assuming that this Option were exercised on such date for such number of shares
and assuming that such shares, together with all other Option Shares held by
Grantee and its affiliates as of such date, were sold for cash at the closing
market price for the Common Stock as of the close of business on the preceding
trading day (less customary brokerage commissions).

         16. The parties hereto acknowledge that damages would be an inadequate
remedy for a breach of this Agreement by either party hereto and that the
obligations of the parties hereto shall be enforceable by either party hereto
through injunctive or other equitable relief.

         17. If any term, provision, covenant or restriction contained in this
Agreement is held by a court or a fed-


                                         12


eral or state regulatory agency of competent jurisdiction to be invalid, void or
unenforceable, the remainder of the terms, provisions and covenants and
restrictions contained in this Agreement shall remain in full force and effect,
and shall in no way be affected, impaired or invalidated.  If for any reason
such court or regulatory agency determines that the Holder is not permitted to
acquire the full number of shares of Common Stock provided in Section 1(a)
hereof (as adjusted pursuant to Section 1(b) or 5 hereof), it is the express
intention of Issuer to allow the Holder to acquire such lesser number of shares
as may be permissible, without any amendment or modification hereof.

         18. All notices, requests, claims, demands and other communications
hereunder shall be deemed to have been duly given when delivered in person, by
cable, telegram, telecopy or telex, or by registered or certified mail (postage
prepaid, return receipt requested) at the respective addresses of the parties
set forth in the Reorganization Agreement.

         19. This Agreement shall be governed by and construed in accordance
with the laws of the State of Delaware, regardless of the laws that might
otherwise govern under applicable principles of conflicts of laws thereof.

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

         21. Except as otherwise expressly provided herein, each of the parties
hereto shall bear and pay all costs and expenses incurred by it or on its behalf
in connection with the transactions contemplated hereunder, including fees and
expenses of its own financial consultants, investment bankers, accountants and
counsel.

         22. Except as otherwise expressly provided herein or in the Merger
Agreements, this Agreement contains the entire agreement between the parties
with respect to the transactions contemplated hereunder and supersedes all prior
arrangements or understandings with respect thereof, written or oral.  The terms
and conditions of this Agreement shall inure to the benefit of and be binding
upon the parties hereto and their respective successors and permitted assigns. 
Nothing in this Agreement, expressed or implied, is intended to confer upon any
party, other than the parties hereto, and their respective successors and
permitted assigns, any rights, remedies, obligations or liabilities under or by
reason of this Agreement, except as expressly provided herein.


                                         13


         23. Capitalized terms used in this Agreement and not defined herein
shall have the meanings assigned thereto in the Merger Agreement.

                                         14

 
              IN WITNESS WHEREOF, each of the parties has caused this Agreement
to be executed on its behalf by its officers thereunto duly authorized, all as
of the date first above written.


                                       ONBANCORP, INC.



                                       By: /s/ Robert J. Bennett          
                                          -----------------------
                                          Name:  Robert J. Bennett
                                          Title: Chairman and Chief    
                                                 Executive Officer


                                       FIRST EMPIRE STATE CORPORATION



                                       By: /s/ Richard A. Lammert         
                                          -----------------------
                                          Name:  Richard A. Lammert
                                          Title: Senior Vice 
                                                 President and          
                                                 General Counsel

                                         15