Exhibit 99.1

                             STOCK OPTION AGREEMENT

                  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 May 16, 2000, Keystone Financial, Inc., a
Pennsylvania corporation ("Issuer"), and M&T Bank 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 9,730,070 fully paid and nonassessable shares of Issuer's Common Stock, par
value $2.00 per share ("Common Stock"), at a price of $15.125 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 outstanding 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 twelve 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
10 hereof be exercised) at any time when Grantee shall be in willful breach of
any of its covenants or 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).

                  (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 "Exchange Act"), and the
rules and regulations thereunder) other than Grantee or any of its Subsidiaries
(each a "Grantee Subsidiary"). For purposes of this Agreement, "Acquisition
Transaction" shall mean (w) a merger or consolidation, or any

                                     - 2 -


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 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) 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;

                           (iii) 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 Exchange 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 beneficially own, directly or
indirectly, 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);

                           (iv) (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, (y) 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

                                     - 3 -


                           (v) 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.

                  (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

                                     - 4 -


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 "Securities 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 Securities 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 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

                                     - 5 -


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. ss. 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 Holder, 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 -


                  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 Securities Act
covering this Option and any shares issued and issuable pursuant to this Option
and shall use its reasonable best efforts to 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 or
Holders shall constitute at least 25% of the total number of shares to be sold
by the Holder or Holders 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 Grantee, 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 than
one Holder as a result of any assignment or division of this Agreement.

                  7. The periods for exercise of certain rights under Sections
2, 6, 10 and 12 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)

                                     - 7 -


to the extent necessary to avoid liability under Section 16(b) of the Exchange
Act by reason of such exercise.

                  8. 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.

                  9. 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 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.

                  10. 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 7); provided, however, that until the date fifteen 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

                                     - 8 -


(proof of which approval shall be furnished promptly to Issuer), 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.

                  11. 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, 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.

                  12. (a) Upon the occurrence of a Subsequent Triggering Event
that occurs prior to an Exercise Termination Event, (i) at the request of any
Holder, delivered within thirty days following such occurrence (or such later
period as provided in Section 7) but in any event prior to an Exercise
Termination Event, Issuer shall repurchase the Option from the Holder at a price
(the "Option Repurchase Price") equal to the amount by which (A) the
market/offer price (as defined below) exceeds (B) the Option Price, multiplied
by the number of shares for which this Option may then be exercised, plus, to
the extent not previously reimbursed, Grantee's reasonable out-of-pocket
expenses incurred in connection with the transactions contemplated by, and the
enforcement of Grantee's rights under, the Merger Agreements, including without
limitation legal, accounting and investment banking fees (the "Grantee's
Out-of-Pocket Expenses"), and (ii) at the request of any owner of Option Shares
from time to time (the "Owner"), delivered within thirty days following such
occurrence (or such later period as provided in Section 7), Issuer shall
repurchase such number of the Option Shares from such Owner as the Owner shall
designate at a price per share ("Option Share Repurchase Price") equal to the
greater of (A) the market/offer price and (B) the average option price per share
paid by the Owner for the Option Shares so designated, plus, to the extent not
previously reimbursed, Grantee's Out-of-Pocket Expenses. The term "market/offer
price" shall mean the highest of (w) the price per share of the Common Stock at
which a tender offer or exchange offer therefor has been made, (x) the price per
share of the Common Stock to be paid by any Person, other than Grantee or a
subsidiary of Grantee, pursuant to an agreement with Issuer, (y) the highest
closing price for shares of Common Stock within the six month period immediately
preceding the required repurchase of Options or Option Shares, as the case may
be, or (z) in the event of a sale of all or substantially all of Issuer's
assets, the sum of the price paid in such sale for such assets and the current
market value of the remaining assets of Issuer as determined by a nationally
recognized investment banking firm selected by a majority in the interest of the
Holders or the Owners, as the case may be, and reasonably acceptable to Issuer,
divided by the number of shares of Common Stock of Issuer outstanding at the
time of

                                     - 9 -


such sale. In determining the market/offer price, the value of consideration
other than cash shall be determined by a nationally recognized investment
banking firm selected by a majority in interest of the Holders or the Owners, as
the case may be, and reasonably acceptable to Issuer.

                  (b) Each Holder and Owner, as the case may be, may exercise
its right to require Issuer to repurchase the Option and any Option Shares
pursuant to this Section 12 by surrendering for such purpose to Issuer, at its
principal office, a copy of this Agreement or certificates for Option Shares, as
applicable, accompanied by a written notice or notices stating that such Holder
or Owner elects to require Issuer to repurchase this Option and/or Option Shares
in accordance with the provisions of this Section 12. As promptly as
practicable, and in any event within ten business days after the surrender of
the Option and/or certificates representing Option Shares and the receipt of
such notice or notices relating thereto, Issuer shall deliver or cause to be
delivered to each Holder the Option Repurchase Price and/or to each Owner the
Option Share Repurchase Price therefor or the portion thereof that Issuer is not
then prohibited under applicable law and regulation from so delivering.

                  (c) To the extent that Issuer is prohibited under applicable
law or regulation, or as a consequence of administrative policy, or as a result
of a written agreement or other binding obligation with a governmental or
regulatory body or agency, from repurchasing the Option and/or the Option Shares
in full, Issuer shall immediately so notify each Holder and/or each Owner and
thereafter deliver or cause to be delivered, from time to time, to such Holder
and/or Owner, as appropriate, the portion of the Option Repurchase Price and the
Option Share Repurchase Price, respectively, that it is no longer prohibited
from delivering, within ten business days after the date on which Issuer is no
longer so prohibited; provided, however, that if Issuer at any time after
delivery of a notice of repurchase pursuant to paragraph (b) of this Section 12
is prohibited under applicable law or regulation, or as a consequence of
administrative policy, from delivering to any Holder and/or Owner, as
appropriate, the Option Repurchase Price and the Option Share Repurchase Price,
respectively, in part or in full (and Issuer hereby undertakes to use its best
efforts to receive any required regulatory and legal approvals and to file any
required notices as promptly as practicable in order to accomplish such
repurchase), such Holder or Owner may revoke its notice of repurchase of the
Option or the Option Shares either in whole or to the extent of the prohibition,
whereupon Issuer shall promptly (i) deliver to such Holder and/or Owner, as
appropriate, that portion of the Option Purchase Price or the Option Share
Repurchase Price that Issuer is not prohibited from delivering; and (ii)
deliver, as appropriate, either (A) to such Holder, a new Stock Option Agreement
evidencing the right of such Holder to purchase that number of shares of Common
Stock obtained by multiplying the number of shares of Common Stock for which the
surrendered Stock Option Agreement was exercisable at the time of delivery of
the notice of repurchase by a fraction, the numerator of which is the Option
Repurchase Price less the portion thereof theretofore delivered to the Holder
and the denominator of which is the Option Repurchase Price, or (B) to such
Owner, a certificate for the Option Shares it is then so prohibited from
repurchasing.

                                     - 10 -


                  13. 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.

                  14. If any term, provision, covenant or restriction contained
in this Agreement is held by a court or a federal 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.

                  15. 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.

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

                  17. 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.

                  18. 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.

                  19. 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.

                                     - 11 -


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

                                     - 12 -


                  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.


KEYSTONE FINANCIAL, INC.


By /s/ Carl L. Campbell
   ------------------------------------
   Carl L. Campbell
   Chairman, President and CEO


M&T BANK CORPORATION


By /s/ Gary S. Paul
   ------------------------------------
   Gary S. Paul
   Senior Vice President

                                     - 13 -