STOCK OPTION AGREEMENT

     STOCK OPTION AGREEMENT, dated June 21, 1999, between UST CORP., a
Massachusetts corporation ("Issuer"), and CITIZENS FINANCIAL GROUP, INC., a
Delaware corporation ("Grantee").

                                  WITNESSETH:

     WHEREAS, Grantee and Issuer have entered into an Agreement and Plan of
Merger of even date herewith (the "Merger Agreement"), which agreement has been
executed by the parties hereto immediately prior to this Agreement; and

     WHEREAS, as a condition to Grantee's entering into the Merger Agreement
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 Agreement, 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 8,541,333
fully paid and nonassessable shares of Issuer's Common Stock, par value $0.625
per share ("Common Stock"), at a price of $24.25 per share (the "Option
Price"); provided further 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
issued or otherwise become outstanding after the date of this Agreement (other
than pursuant to this Agreement), the number of shares of Common Stock subject
to the Option shall be increased so that, after such issuance, it 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 Agreement.

     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 that the Holder shall have
sent the written notice of such exercise (as provided in subsection (e) of this
Section 2) within 100 days following such Subsequent Triggering Event. Each of
the following shall be an "Exercise Termination Event": (i) the Effective Time
(as defined in the Merger Agreement) of the Merger; (ii) termination of the

Merger Agreement 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 8.1(d) of the Merger Agreement
(unless the breach by Issuer giving rise to such right of termination is
non-volitional); or (iii) the passage of eighteen months after termination of
the Merger Agreement if such termination follows the occurrence of an Initial
Triggering Event or is a termination by Grantee pursuant to Section 8.1(d) of
the Merger Agreement (unless the breach by Issuer giving rise to such right of
termination is non-volitional)(provided that if an Initial Triggering Event
continues or occurs beyond such termination and prior to the passage of such
eighteen-month period, the Exercise Termination Event shall be twelve months
from the expiration of the Last Triggering Event but in no event more than
eighteen months after such termination). The "Last Triggering Event" shall mean
the last Initial Triggering Event to expire. The term "Holder" shall mean the
holder or holders of the Option.

          (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 the Board of Directors of Issuer shall have
recommended that the stockholders of Issuer approve or accept any Acquisition
Transaction or shall have failed to publicly oppose an Acquisition Transaction,
in each case with any person other than Grantee or a Grantee Subsidiary. 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 of all or a substantial portion of the
assets 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 any Significant Subsidiary of Issuer, or (z) any substantially similar
transaction; provided, however, that in no event shall any merger,
consolidation, purchase, liquidation, dividend in kind, reorganization or
similar transaction involving only the Issuer and one or more of its
Subsidiaries or involving only any two or more of such Subsidiaries, be deemed
to be an Acquisition Transaction, provided any such transaction is not entered
into in violation of the terms of the Merger Agreement;

               (ii) Issuer or any Issuer Subsidiary, 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
Grantee Subsidiary, or the Board of Directors of Issuer shall have publicly
withdrawn or modified, or publicly announced its intention to withdraw or
modify, in any manner adverse to Grantee, its recommendation that the
stockholders of Issuer approve the transactions contemplated by the Merger
Agreement;

               (iii) The shareholders of Issuer shall have voted and failed to
approve and adopt the Merger Agreement and the Merger at a meeting which has
been held for that purpose or any adjournment or postponement thereof, or such
meeting shall not have been held in violation of the Merger Agreement or shall
have been canceled prior to termination of the Merger Agreement if, prior to
such meeting (or if such meeting shall not have been held or shall have been
canceled, prior to such termination), any person (other than the Grantee or a
Grantee Subsidiary) shall have made a proposal to Issuer or its stockholders by
public announcement or written communication that is or becomes the subject of
public disclosure to engage in an Acquisition Transaction;

               (iv) Any person other than Grantee, any Grantee Subsidiary or
any Issuer Subsidiary acting in a fiduciary capacity in the ordinary course of
its business 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 Option Agreement having
the meaning assigned thereto in Section 13(d) of the 1934 Act, and the rules
and regulations thereunder);

               (v) Any person other than Grantee or any Grantee Subsidiary
shall have made a bona fide proposal to Issuer or its stockholders by public
announcement or written communication that is or becomes the subject of public
disclosure to engage in an Acquisition Transaction;

               (vi) 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 Merger Agreement and such
breach (x) would entitle Grantee to terminate the Merger Agreement and (y)
shall not have been cured prior to the Notice Date (as defined below); or

               (vii) Any person other than Grantee or any Grantee Subsidiary,
other than in connection with a transaction to which Grantee has given its
prior written consent, shall have filed an application or notice with the
Federal Reserve Board, or other federal or state bank regulatory authority,
whether in draft or final form, for approval to engage in an Acquisition
Transaction.

          (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 20%
or more of the then outstanding Common Stock; or
               (ii) The occurrence of the Initial Triggering Event described in
clause (i) of subsection (b) of this Section 2, except that the percentage
referred to in clause (y) shall be 20%.

          (d) Issuer shall notify Grantee promptly in writing of the occurrence
of any Initial Triggering Event or Subsequent Triggering Event (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 (including any extensions thereof) have
expired or been terminated or such approvals have been obtained and any
requisite waiting period or periods (including any extensions thereof) 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 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 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. sec. 18a and regulations promulgated
thereunder and (y) in the event, under the Bank Holding Company Act of 1956, as
amended (the "BHCA"), or the Change in Bank Control Act of 1978, as amended, or
any state banking law, prior approval of or notice to the Federal Reserve Board
or to 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. 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 100 day after 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 shelf registration statement under the 1933
Act covering the resale of this Option and any shares issued pursuant to this
Option and the issuance of any shares issuable pursuant to this Option to the
extent then permitted under the rules, regulations or policies of the SEC and,
to the extent not so permitted, the resale of such shares issuable pursuant to
this Option. The Issuer 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 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 practical 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 such 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 than one Grantee as a result of any assignment or division
of this Agreement.

     7. (a) Immediately prior to the occurrence of a Repurchase Event (as
defined below), (i) following a request of the Holder, delivered prior to an
Exercise Termination Event, Issuer (or any successor thereto) 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 and (ii) at the request of the owner of Option Shares from
time to time (the "Owner") delivered within 100 days after such occurrence (or
such later period as provided in Section 10), Issuer shall repurchase such
number of the Option Shares from the Owner as the Owner shall designate at a
price (the "Option Share Repurchase Price") equal to the market/offer price
multiplied by the number of Option Shares so designated. The term "market/offer
price" shall mean the highest of (i) the price per share of Common Stock at
which a tender offer or exchange offer therefor has been made, (ii) the price
per share of Common Stock to be paid by any third party pursuant to an
agreement with Issuer, (iii) the highest closing price for shares of Common
Stock within the six-month period immediately preceding the date the Holder
gives notice of the required repurchase of this Option or the Owner gives
notice of the required repurchase of Option Shares, as the case may be, or (iv)
in the event of a sale of all or a substantial portion 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 the Holder or the Owner, as the case may
be, divided by the number of shares of Common Stock of Issuer outstanding at
the time of 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 the Holder or Owner, as the case may be,
and reasonably acceptable to the Issuer.

          (b) The Holder and the 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 7 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 the Holder
or the Owner, as the case may be, elects to require Issuer to repurchase this
Option and/or the Option Shares in accordance with the provisions of this

Section 7. Within the later to occur of (x) five business days after the
surrender of the Option and/or certificates representing Option Shares and the
receipt of such notice or notices relating thereto and (y) the time that is
immediately prior to the occurrence of a Repurchase Event, Issuer shall deliver
or cause to be delivered to the Holder the Option Repurchase Price and/or to
the 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 from repurchasing the Option and/or the Option Shares in full,
Issuer shall immediately so notify the Holder and/or the Owner and thereafter
deliver or cause to be delivered, from time to time, to the Holder and/or the
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 five 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 7
is prohibited under applicable law or regulation from delivering to the Holder
and/or the Owner, as appropriate, the Option Repurchase Price and the Option
Share Repurchase Price, respectively, in full (and Issuer hereby undertakes to
use its best efforts to obtain all required regulatory and legal approvals and
to file any required notices as promptly as practicable in order to accomplish
such repurchase), the 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, in the latter case, Issuer shall promptly (i) deliver
to the Holder and/or the Owner, as appropriate, that portion of the Option
Repurchase Price or the Option Share Repurchase Price that Issuer is not
prohibited from delivering; and (ii) deliver, as appropriate, either (A) to the
Holder, a new Stock Option Agreement evidencing the right of the 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 the Owner a certificate for the
Option Shares it is then so prohibited from repurchasing.

          (d) For purposes of this Section 7, a Repurchase Event shall be
deemed to have occurred (i) upon the consummation of any merger, consolidation
or similar transaction involving Issuer or any purchase, lease or other
acquisition of all or a substantial portion of the assets of Issuer, other than
any such transaction which would not constitute an Acquisition Transaction
pursuant to the proviso to Section 2 (b) (i) hereof or (ii) upon the
acquisition by any person of beneficial ownership of 50% or more of the then
outstanding shares of Common Stock, provided that no such event shall
constitute a Repurchase Event unless a Subsequent Triggering Event shall have
occurred prior to an Exercise Termination Event. The parties hereto agree that
Issuer's obligations to repurchase the Option or Option Shares under this
Section 7 shall not terminate upon the occurrence of an Exercise Termination
Event unless no Subsequent Triggering Event shall have occurred prior to the
occurrence of an Exercise Termination Event.

     8. (a) In the event that prior to an Exercise Termination Event, Issuer
shall enter into an agreement (i) to consolidate with or merge into any person,

other than Grantee or one of its Subsidiaries, and shall not be the continuing
or surviving corporation of such consolidation or merger, (ii) to permit any
person, other than Grantee or one of its Subsidiaries, to merge into Issuer and
Issuer shall be the continuing or surviving corporation, but, in connection
with such merger, the then outstanding shares of Common Stock shall be changed
into or exchanged for stock or other securities of any other person or cash or
any other property or the then outstanding shares of Common Stock shall after
such merger represent less than 50% of the outstanding voting shares and voting
share equivalents of the merged company, or (iii) to sell or otherwise transfer
all or substantially all of its assets to any person, other than Grantee or one
of its Subsidiaries, then, and in each such case, the agreement governing such
transaction shall make proper provision so that the Option shall, upon the
consummation of any such transaction and upon the terms and conditions set
forth herein, be converted into, or exchanged for, an option (the "Substitute
Option"), at the election of the Holder, of either (x) the Acquiring
Corporation (as hereinafter defined) or (y) any person that controls the
Acquiring Corporation.

          (b) The following terms have the meanings indicated:

               (1) "Acquiring Corporation" shall mean (i) the continuing or
surviving corporation of a consolidation or merger with Issuer (if other than
Issuer), (ii) Issuer in a merger in which Issuer is the continuing or surviving
person, and (iii) the transferee of all or substantially all of Issuer's
assets.

               (2) "Substitute Common Stock" shall mean the common stock issued
by the issuer of the Substitute Option upon exercise of the Substitute Option.

               (3) "Assigned Value" shall mean the market/offer price, as
defined in Section 7.

               (4) "Average Price" shall mean the average closing price of a
share of the Substitute Common Stock for the one year immediately preceding the
consolidation, merger or sale in question, but in no event higher than the
closing price of the shares of Substitute Common Stock on the day preceding
such consolidation, merger or sale; provided that if Issuer is the issuer of
the Substitute Option, the Average Price shall be computed with respect to a
share of common stock issued by the person merging into Issuer or by any
company which controls or is controlled by such person, as the Holder may
elect.

          (c) The Substitute Option shall have the same terms as the Option,
provided, that if the terms of the Substitute Option cannot, for legal reasons,
be the same as the Option, such terms shall be as similar as possible and in no
event less advantageous to the Holder. The issuer of the Substitute Option
shall also enter into an agreement with the then Holder or Holders of the
Substitute Option in substantially the same form as this Agreement, which shall
be applicable to the Substitute Option.

          (d) The Substitute Option shall be exercisable for such number of
shares of Substitute Common Stock as is equal to the Assigned Value multiplied
by the number of shares of Common Stock for which the Option is then
exercisable, divided by the Average Price. The exercise price of the Substitute

Option per share of Substitute Common Stock shall then be equal to the Option
Price multiplied by a fraction, the numerator of which shall be the number of
shares of Common Stock for which the Option is then exercisable and the
denominator of which shall be the number of shares of Substitute Common Stock
for which the Substitute Option is exercisable.

          (e) In no event, pursuant to any of the foregoing paragraphs, shall
the Substitute Option be exercisable for more than 19.9% of the shares of
Substitute Common Stock outstanding prior to exercise of the Substitute Option.
In the event that the Substitute Option would be exercisable for more than
19.9% of the shares of Substitute Common Stock outstanding prior to exercise
but for this clause (e), the issuer of the Substitute Option (the "Substitute
Option Issuer") shall make a cash payment to Holder equal to the excess of (i)
the value of the Substitute Option without giving effect to the limitation in
this clause (e) over (ii) the value of the Substitute Option after giving
effect to the limitation in this clause (e). This difference in value shall be
determined by a nationally recognized investment banking firm selected by the
Holder or the Owner, as the case may be, and reasonably acceptable to the
Acquiring Corporation.

          (f) Issuer shall not enter into any transaction described in
subsection (a) of this Section 8 unless the Acquiring Corporation and any
person that controls the Acquiring Corporation assume in writing all the
obligations of Issuer hereunder.

     9. (a) At the request of the holder of the Substitute Option (the
"Substitute Option Holder"), the issuer of the Substitute Option (the
"Substitute Option Issuer") shall repurchase the Substitute Option from the
Substitute Option Holder at a price (the "Substitute Option Repurchase Price")
equal to (x) the amount by which (i) the Highest Closing Price (as hereinafter
defined) exceeds (ii) the exercise price of the Substitute Option, multiplied
by the number of shares of Substitute Common Stock for which the Substitute
Option may then be exercised plus (y) Grantee's Out-of-Pocket Expenses (to the
extent not previously reimbursed), and at the request of the owner (the
"Substitute Share Owner") of shares of Substitute Common Stock (the "Substitute
Shares"), the Substitute Option Issuer shall repurchase the Substitute Shares
at a price (the "Substitute Share Repurchase Price") equal to (x) the Highest
Closing Price multiplied by the number of Substitute Shares so designated plus
(y) Grantee's Out-of-Pocket Expenses (to the extent not previously reimbursed).
The term "Highest Closing Price" shall mean the highest closing price for
shares of Substitute Common Stock within the six-month period immediately
preceding the date the Substitute Option Holder gives notice of the required
repurchase of the Substitute Option or the Substitute Share Owner gives notice
of the required repurchase of the Substitute Shares, as applicable.

          (b) The Substitute Option Holder and the Substitute Share Owner, as
the case may be, may exercise its respective right to require the Substitute
Option Issuer to repurchase the Substitute Option and the Substitute Shares
pursuant to this Section 9 by surrendering for such purpose to the Substitute
Option Issuer, at its principal office, the agreement for such Substitute
Option (or, in the absence of such an agreement, a copy of this Agreement) and
certificates for Substitute Shares accompanied by a written notice or notices
stating that the Substitute Option Holder or the Substitute Share Owner, as the
case may be, elects to require the Substitute Option Issuer to repurchase the

Substitute Option and/or the Substitute Shares in accordance with the
provisions of this Section 9. As promptly as practicable, and in any event
within five business days after the surrender of the Substitute Option and/or
certificates representing Substitute Shares and the receipt of such notice or
notices relating thereto, the Substitute Option Issuer shall deliver or cause
to be delivered to the Substitute Option Holder the Substitute Option
Repurchase Price and/or to the Substitute Share Owner the Substitute Share
Repurchase Price therefor or the portion thereof which the Substitute Option
Issuer is not then prohibited under applicable law and regulation from so
delivering.

          (c) To the extent that the Substitute Option Issuer is prohibited
under applicable law or regulation from repurchasing the Substitute Option
and/or the Substitute Shares in part or in full, the Substitute Option Issuer
shall immediately so notify the Substitute Option Holder and/or the Substitute
Share Owner and thereafter deliver or cause to be delivered, from time to time,
to the Substitute Option Holder and/or the Substitute Share Owner, as
appropriate, the portion of the Substitute Share Repurchase Price,
respectively, which it is no longer prohibited from delivering, within five
business days after the date on which the Substitute Option Issuer is no longer
so prohibited; provided, however, that if the Substitute Option Issuer is at
any time after delivery of a notice of repurchase pursuant to subsection (b) of
this Section 9 prohibited under applicable law or regulation from delivering to
the Substitute Option Holder and/or the Substitute Share Owner, as appropriate,
the Substitute Option Repurchase Price and the Substitute Share Repurchase
Price, respectively, in full (and the Substitute Option Issuer shall use its
best efforts to receive all required regulatory and legal approvals as promptly
as practicable in order to accomplish such repurchase), the Substitute Option
Holder or Substitute Share Owner may revoke its notice of repurchase of the
Substitute Option or the Substitute Shares either in whole or to the extent of
the prohibition, whereupon, in the latter case, the Substitute Option Issuer
shall promptly (i) deliver to the Substitute Option Holder or Substitute Share
Owner, as appropriate, that portion of the Substitute Option Repurchase Price
or the Substitute Share Repurchase Price that the Substitute Option Issuer is
not prohibited from delivering; and (ii) deliver, as appropriate, either (A) to
the Substitute Option Holder, a new Substitute Option evidencing the right of
the Substitute Option Holder to purchase that number of shares of the
Substitute Common Stock obtained by multiplying the number of shares of the
Substitute Common Stock for which the surrendered Substitute Option was
exercisable at the time of delivery of the notice of repurchase by a fraction,
the numerator of which is the Substitute Option Repurchase Price less the
portion thereof theretofore delivered to the Substitute Option Holder and the
denominator of which is the Substitute Option Repurchase Price, or (B) to the
Substitute Share Owner, a certificate for the Substitute Option Shares it is
then so prohibited from repurchasing.

     10. The 100-day period for exercise of certain rights under Sections 2, 6,
7 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.

          (c) Issuer has taken all action (including if required redeeming all
of the Rights or amending or terminating the Rights Agreement) so that the
entering into of this Option Agreement, the acquisition of shares of Common
Stock hereunder and the other transactions contemplated hereby do not and will
not result in the grant of any rights to any person under the Rights Agreement
or enable or require the Rights to be exercised, distributed or triggered.

     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 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 Option 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 90
days 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 under the BHCA 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 Stock Market
upon official notice of issuance and applying to the Federal Reserve Board
under the BHCA 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.

     15. (a) Grantee may, at any time during which Issuer would be required to
repurchase the Option or any Option Shares pursuant to Section 7, surrender the
Option (together with any Option Shares issued to and then owned by Grantee) to
Issuer in exchange for a cash fee equal to the Surrender Price (as defined
below); provided, however, that Grantee may not exercise its rights pursuant to
this Section 15 if Issuer has repurchased the Option (or any portion thereof)
or any Option Shares pursuant to Section 7. The "Surrender Price" shall be
equal to (i) $56.3 million, plus (ii) if applicable, the aggregate purchase
price previously paid pursuant hereto by Grantee with respect to any Option
Shares, minus (iii) if applicable, the sum of (A) the excess of (1) the net
cash amounts, if any, received by Grantee pursuant to the arms' length sale of
Option Shares (or any other securities into which such Option Shares were
converted or exchanged) to any party not affiliated with Grantee, over (2) the
aggregate purchase price previously paid pursuant hereto by Grantee with
respect to such Option Shares and (B) the net cash amounts, if any, received by
Grantee pursuant to an arms' length sale of a portion of the Option to any
party not affiliated with Grantee.

          (b) Grantee may exercise its right to surrender the Option and any
Option Shares pursuant to this Section 15 by surrendering to Issuer, at its
principal office, this Agreement together with certificates for Option Shares,
if any, accompanied by a written notice stating (i) that Grantee elects to
surrender the Option and Option Shares, if any, in accordance with the
provisions of this Section 15 and (ii) the Surrender Price. The Surrender Price
shall be payable in immediately available funds on or before the second
business day following receipt of such notice by Issuer.

          (c) To the extent that Issuer is prohibited under applicable law or
regulation from paying the Surrender Price to Grantee in full, Issuer shall
immediately so notify Grantee and thereafter deliver or cause to be delivered,
from time to time, to Grantee, the portion of the Surrender Price that Issuer
is no longer prohibited from paying, within five 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 surrender pursuant to paragraph (b)
of this Section 15 is prohibited under applicable law or regulation from paying

to Grantee the Surrender Price in full (i) Issuer shall (A) use its reasonable
best efforts to obtain all required regulatory and legal approvals and to file
any required notices as promptly as practicable in order to make such payments,
(B) within five days of the submission or receipt of any documents relating to
any such regulatory and legal approvals, provide Grantee with copies of the
same, and (C) keep Grantee advised of both the status of any such request for
regulatory and legal approvals, as well as any discussions with any relevant
regulatory or other third party reasonably related to the same and (ii) Grantee
may revoke such notice of surrender by delivery of a notice of revocation to
Issuer and, upon delivery of such notice of revocation, the Exercise
Termination Date shall be extended to a date six months from the date on which
the Exercise Termination Date would have occurred if not for the provisions of
this Section 15(c) (during which period Grantee may exercise any of its rights
hereunder, including any and all rights pursuant to this Section 15).

          (d) Grantee shall have rights substantially identical to those set
forth in paragraphs (a), (b) and (c) of this Section 15 with respect to the
Substitute Option and the Substitute Option Issuer during any period in which
the Substitute Option Issuer would be required to repurchase the Substitute
option pursuant to Section 9.

     16. (a) 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
$77.4 million; provided that nothing in this sentence shall restrict any
exercise of the Option permitted hereby on any subsequent date.

          (b) 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 (as defined below) 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).

          (c) As used herein, the term "Total Profit" shall mean the aggregate
amount (before taxes) of the following: (i) the amount received by Grantee
pursuant to Issuer's repurchase of the Option (or any portion thereof) pursuant
to Section 7, (ii) (x) the amount received by Grantee pursuant to Issuer's
repurchase of Option Shares (or any portion thereof) pursuant to Section 7,
less (y) the Grantee's purchase price for such Option Shares, (iii) 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, (iv) any amounts received by Grantee on the transfer of the Option (or
any portion thereof) to any unaffiliated party, and (v) any amount equivalent
to the foregoing with respect to the Substitute Option.

     17. 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.

     18. 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, or Issuer is not
permitted to repurchase pursuant to Section 7, 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 or to require Issuer to repurchase such lesser number of shares as may
be permissible, without any amendment or modification hereof.

     19. 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 Merger Agreement.

     20. This Agreement shall be governed by and construed in accordance with
the laws of the Commonwealth of Massachusetts regardless of the laws that might
otherwise govern under applicable principles of conflicts of laws thereof.

     21. 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.

     22. 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.

     23. Except as otherwise expressly provided herein or in the Merger
Agreement, 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
except as assigns, any rights, remedies, obligations or liabilities under or by
reason of this Agreement, except as expressly provided herein.

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



     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.

                                       UST CORP.


                                   By:  /s/ Neal F. Finnegan
                                        -------------------------
                                   Name:  Neal F. Finnegan
                                   Title: President and Chief Executive Officer


                                       CITIZENS FINANCIAL
                                       GROUP, INC.


                                   By: /s/ Lawrence K. Fish
                                       ----------------------
                                   Name:  Lawrence K. Fish
                                   Title: Chairman, President and Chief
                                          Executive Officer