<PAGE>
 
EXHIBIT 10.2
                             STOCK OPTION AGREEMENT


     This STOCK OPTION AGREEMENT ("Option Agreement") dated as of the 12th day
of September, 1997, by and between WESBANCO, INC., a West Virginia corporation
("Wesbanco") and COMMERCIAL BANCSHARES, INCORPORATED, a West Virginia
corporation ("Commercial").

WITNESSETH:


     WHEREAS, the Boards of Directors of Wesbanco and Commercial have approved a
Binding Letter of Intent ("Agreement"), which contemplates the merger of
Commercial with and into CBI Corporation, a West Virginia corporation and
wholly-owned subsidiary of Wesbanco ("CBI"), with CBI continuing as the
surviving corporation; subject to the execution of a definitive merger agreement
which the parties agree to negotiate in good faith, and

     WHEREAS, as a condition to Wesbanco's entry into the Agreement and to
induce such entry, Commercial has agreed to grant to Wesbanco the option set
forth herein to purchase authorized but unissued shares of common stock, par
value $5.00 per share of Commercial ("Commercial Common Stock");

     NOW, THEREFORE, in consideration of the premises herein contained, the
parties agree as follows:

     1.  Definitions.  Capitalized terms which are to be defined in the Merger
Agreement and used herein shall have the same meanings as in the Merger
Agreement.  The parties have prepared a draft of said Merger Agreement and
incorporate the referenced provisions of said draft language into this Agreement
as if set forth herein verbatim.  A copy of said draft Merger Agreement is
attached hereto as Exhibit A (hereinafter "Merger Agreement").

     2.  Grant of Option.  Subject to the terms and conditions set forth herein,
Commercial hereby grants to Wesbanco an option ("Option") to purchase up to
321,620 shares of Commercial Common Stock, at a price of $50.00 per share (the
"Option Price") payable in cash as provided in Section 4 hereof; provided,
however, that in the event Commercial issues or agrees to issue any shares of
Commercial Common Stock (other than as permitted under the Agreement) at a price
less than $50.00 per share (as adjusted pursuant to Section 6 hereof), the
exercise price shall be equal to such lesser price.

     3.  Exercise of Option.

        a. Provided that Wesbanco is not in material breach of the agreements
     and covenants contained in the Agreement, Wesbanco may exercise the Option,
     in whole or in part, at any time or from time to time if a Purchase Event
     (as defined below) shall have occurred and be continuing; provided that to
     the extent the Option shall not have been exercised, it shall terminate and
     be of no further force and effect (i) on the Effective Date of the Merger
     or (ii) upon termination of the Merger Agreement in accordance with the
     provisions thereof (other than a termination resulting from a willful
     breach by Commercial of Section 7.21(d) of the Merger Agreement or,
     following the occurrence of a Purchase Event, failure of Commercial's
     shareholders to approve the Merger Agreement by the vote required under
     applicable law), or (iii) six months after termination of the Merger
     Agreement due to a willful breach by Commercial of Section 7.21(d) of the
     Merger Agreement or, following the occurrence of a Purchase Event, failure
     of Commercial's shareholders to approve the Merger Agreement by the vote
     required under applicable law; and provided further that any such exercise
     shall be subject to compliance with applicable provisions of law.
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        b.  As used herein, a "Purchase Event" shall mean any of the following
     events or transactions occurring after the date hereof:

                (i) any person (other than Commercial, any Commercial
          Subsidiary, Wesbanco or any affiliate of Wesbanco) shall have
          commenced a bona fide tender or exchange offer to purchase shares of
          Commercial Common Stock such that upon consummation of such offer such
          person would own or control 15% or more of the outstanding shares of
          Commercial Common Stock;

                (ii) any person (other than Commercial or any Commercial
          Subsidiary), other than in connection with a transaction to which
          Wesbanco has given its prior written consent, shall have filed an
          application or notice with any federal or state regulatory agency for
          clearance or approval, to (x) merge or consolidate, or enter into any
          similar transaction, with Commercial or any Commercial Subsidiary, (y)
          purchase, lease or otherwise acquire all or substantially all of the
          assets of Commercial or any Commercial Subsidiary or (z) purchase or
          otherwise acquire (including by way of merger, consolidation, share
          exchange or any similar transaction) securities representing 51% or
          more of the voting power of Commercial or any Commercial Subsidiary;

                (iii) any person (other than Commercial, any Commercial
          Subsidiary, the Commercial Subsidiaries in a fiduciary capacity,
          Wesbanco, affiliates of Wesbanco or subsidiaries of Wesbanco in a
          fiduciary capacity) shall have acquired after the date hereof
          beneficial ownership or the right to acquire beneficial ownership of
          15% or more of the outstanding shares of Commercial Common Stock (the
          term "beneficial ownership" for purposes of this Option Agreement
          having the meaning assigned thereto in Section 13(d) of the Exchange
          Act and the regulations promulgated thereunder);

                (iv) any person (other than Commercial or any Commercial
          Subsidiary) shall have made a bona fide proposal to Commercial by
          public announcement or written communication that is or becomes the
          subject of public disclosure to (x) acquire Commercial or any
          Commercial Subsidiary by merger, consolidation, purchase of all or
          substantially all of its assets or any other similar transaction, or
          (y) make an offer described in clause (i) above; or

                (v) Commercial shall have willfully breached Section 7.21(d) of
          the Merger Agreement, which breach would entitle Wesbanco to terminate
          such Merger Agreement and such breach shall not have been cured prior
          to the Notice Date (as defined below).

If more than one of the transactions giving rise to a Purchase Event under this
Section 3(b) is undertaken or effected, then all such transactions shall give
rise only to one Purchase Event, which Purchase Event shall be deemed continuing
for all purposes hereunder until all such transactions are abandoned.  As used
in this Option Agreement, "person" shall have the meanings specified in Sections
3(a)(9) and 13(d)(3) of the Exchange Act.

        c. In the event Wesbanco wishes to exercise the Option, it shall send to
     Commercial a written notice (the date of which being herein referred to as
     "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 ("Closing Date"); provided that if prior
     notification to or approval of any federal or state regulatory agency is
     required in connection with such purchase, Wesbanco 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
     period has expired or been terminated or such approval has been obtained
     and any requisite waiting period shall have passed.
<PAGE>
 
     4.  Payment and Delivery of Certificates.

        a. At the closing referred to in Section 3(c) hereof, Wesbanco shall pay
     to Commercial the aggregate purchase price for the shares of Commercial
     Common Stock purchased pursuant to the exercise of the Option in
     immediately available funds by a wire transfer to a bank account designated
     by Commercial.

        b. At such closing, simultaneously with the delivery of cash as provided
     in subsection (a), Commercial shall deliver to Wesbanco a certificate or
     certificates representing the number of shares of Commercial Common Stock
     purchased by Wesbanco, and Wesbanco shall deliver to Commercial a letter
     agreeing that Wesbanco will not offer to sell or otherwise dispose of such
     shares in violation of applicable law or the provisions of this Option
     Agreement.

        c.  Certificates for Commercial Common Stock delivered at a closing
     hereunder may be endorsed with a restrictive legend which 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
Commercial Bancshares, Incorporated and to resale restrictions arising under the
Securities Act of 1933, as amended, a copy of which agreement is on file at the
principal office of Commercial Bancshares, Incorporated.  A copy of such
agreement will be provided to the holder hereof without charge upon receipt by
Commercial Bancshares, Incorporated of a written request."

It is understood and agreed that the above legend shall be removed by delivery
of substitute certificate(s) without such legend if Wesbanco shall have
delivered to Commercial a copy of a letter from the staff of the Securities and
Exchange Commission, or an opinion of counsel, in form and substance reasonably
satisfactory to Commercial, to the effect that such legend is not required for
purposes of the Securities Act.

     5.  Representations.  Commercial hereby represents, warrants and covenants
to Wesbanco as follows:

        a.  Commercial shall at all times maintain sufficient authorized but
     unissued shares of Commercial Common Stock so that the Option may be
     exercised without authorization of additional shares of Commercial  Common
     Stock.

        b. The shares to be issued upon due exercise, in whole or in part, of
     the Option, when paid for as provided herein, will be duly authorized,
     validly issued, fully paid and nonassessable.

     6.  Adjustment Upon Changes in Capitalization.  In the event of any change
in Commercial Common Stock by reason of stock dividends, split-ups, mergers,
recapitalizations, combinations, exchanges of shares or the like, the type and
number of shares subject to the Option, and the purchase price per share, as the
case may be, shall be adjusted appropriately.  In the event that any additional
shares of Commercial Common Stock are issued or otherwise become outstanding
after the date of this Option Agreement (other than pursuant to this Option
Agreement), the number of shares of Commercial Common Stock subject to the
Option shall be adjusted so that, after such issuance, it equals 19.9% of the
number of shares of Commercial Common Stock then issued and outstanding without
giving effect to any shares subject or issued pursuant to the Option.  Nothing
contained in this Section 6 shall be deemed to authorize Commercial to breach
any provision of the Merger Agreement.
<PAGE>
 
     7.  Registration Rights.  Commercial shall, if requested by Wesbanco, as
expeditiously as possible file a registration statement on a form of general use
under the Securities Act if necessary in order to permit the sale or other
disposition of the shares of Commercial Common Stock that have been acquired
upon exercise of the Option in accordance with the intended method of sale or
other disposition requested by Wesbanco.  Wesbanco shall provide all information
reasonably requested by Commercial for inclusion in any registration statement
to be filed hereunder.  Commercial will use its best efforts to cause such
registration statement first to become effective and then to remain effective
for such period not in excess of 270 days from the day such registration
statement first becomes effective as may be reasonably necessary to effect such
sales or other dispositions.  In no event shall Commercial be required to effect
more than two registrations hereunder.  All expenses of registrations hereunder
shall be borne equally by Commercial and Wesbanco.  The filing of any
registration statement hereunder may be delayed for such period of time as may
reasonably be required to facilitate any public distribution by Commercial of
Commercial Common Stock.  If requested by Wesbanco, in connection with any such
registration, Commercial will 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.  Upon receiving any
request from Wesbanco or assignee thereof under this Section 7, Commercial
agrees to send a copy thereof to Wesbanco and to any assignee thereof known to
Commercial, in each case by promptly mailing the same, postage prepaid, to the
address of record of the persons entitled to receive such copies.

     8.  Severability.  If any term, provision, covenant or restriction
contained in this Option 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 Option 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 Option will not
permit the holder to acquire the full number of shares of Commercial Common
Stock provided in Section 2 hereof (as adjusted pursuant to Section 6 hereof),
it is the express intention of Commercial to allow the holder to acquire such
lesser number of shares as may be permissible, without any amendment or
modification hereof.

     9.  Put-Back Rights.

        a.  Upon the consummation of any Purchase Event described in Section
     3(b)(ii) or (v) hereof such that (i) a merger, consolidation, purchase,
     lease or acquisition of all or substantially all of the assets of
     Commercial , purchase or other acquisition of securities representing 51%
     or more of the voting power of Commercial or any Commercial Subsidiary has
     been consummated, or (ii) a willful breach under Section 7.21(d) of the
     Merger Agreement has occurred so that Wesbanco would be entitled to
     terminate the Merger Agreement, and prior to the expiration of the Option
     in accordance with the terms hereof, at the request of Wesbanco, Commercial
     shall repurchase the Option from Wesbanco at a price (the "Repurchase
     Price") equal to the difference between the market/offer price (as defined
     below) for shares of Commercial Common Stock and the Option Price,
     multiplied by the number of shares for which the Option being surrendered
     hereunder may then be exercised but only if the market/offer price is
     greater than the Option Price (the market/offer price is defined as the
     higher of the price per share at which a tender offer or exchange offer for
     51% or more of the voting securities of Commercial has been made and
     consummated, the price per share actually paid by any third party pursuant
     to an agreement that has been consummated whereby Commercial has been
     merged, consolidated with or otherwise acquired by a third party, and the
     highest closing price for Commercial Common Stock within the four-month
     period immediately preceding the date Wesbanco gives written notice of the
     required repurchase of the Option pursuant to this Section 9).  In the
     event that an exchange offer is made or an agreement is entered into for a
     merger or consolidation involving consideration other than cash, the value
     of the securities or other property issuable or deliverable in exchange for
     Commercial Common shall be determined by a nationally recognized investment
     banking firm mutually acceptable to the parties hereto.
<PAGE>
 
        b. Wesbanco may exercise its right to require Commercial to repurchase
     the Option pursuant to this Section 9 by giving Commercial written notice
     of its exercise of its repurchase right in accordance with the provisions
     of this Section 9. Subject to the last proviso of paragraph 9(c) below, as
     promptly as practicable, and in any event within five business days after
     the receipt of such notice or notices relating thereto, Commercial shall
     deliver or cause to be delivered to Wesbanco the Repurchase Price for the
     Option or the portion thereof which Commercial is not then prohibited under
     applicable law and regulation from so delivering.

        c.  To the extent that Commercial is prohibited under applicable law or
     regulation, or as a result of administrative or judicial action, from
     repurchasing the Option in full, Commercial shall immediately so notify
     Wesbanco and thereafter deliver or cause to be delivered, from time to
     time, to Wesbanco, as appropriate, the portion of the Repurchase Price
     which it is no longer prohibited from delivering, within five business days
     after the date on which Commercial is no longer so prohibited, provided,
     however, that to the extent that Commercial is at the time and after the
     expiration of 12 months, so prohibited from delivering to Wesbanco, the
     Repurchase Price, in full (and Commercial hereby undertakes to use its best
     efforts to receive all required regulatory and legal approvals as promptly
     as practicable), Commercial shall deliver to Wesbanco a new Option
     evidencing the right of Wesbanco to purchase that number of shares of
     Commercial Common Stock obtained by multiplying the number of shares of
     Commercial Common Stock for which the Option may at such time be exercised
     by a fraction, the numerator of which is the Repurchase Price less the
     portion thereof (if any) theretofore delivered to the Holder and the
     denominator of which is the Repurchase Price, and Commercial shall have no
     further obligation to repurchase such new Option; and provided, further,
     that upon receipt of such notice and until five days thereafter Wesbanco
     may revoke its notice of repurchase of the Option by written notice to
     Commercial at its principal office stating that Wesbanco elects to revoke
     its election to exercise its rights to require Commercial to repurchase the
     Option, whereupon Commercial will promptly deliver to Wesbanco the Option
     and Commercial shall have no further obligation to repurchase such Option.

     10.  First Refusal.  If at any time during the eighteen months immediately
following the first purchase of shares of Commercial Common Stock pursuant to
the Option, Wesbanco shall desire to sell, assign, transfer or otherwise dispose
of all or any of the shares of Commercial Common Stock acquired by it pursuant
to the Option other than in accordance with the put-back rights in Section 9
hereof, it shall give Commercial written notice of the proposed transaction
("Offeror's Notice"), identifying the proposed transferee and setting forth the
terms of the proposed transaction.  An Offeror's Notice shall be deemed an offer
by Wesbanco to Commercial, which may be accepted within ten business days of the
receipt of such Offeror's Notice, on the same terms and conditions and at the
same price at which Wesbanco is proposing to transfer such shares to a third
party.  Settlement for any shares purchased by Commercial shall be within 15
business days of the date of the acceptance of the offer and the purchase price
shall be paid to Wesbanco in immediately available funds; provided that if prior
notification to or approval of any federal or state regulatory authority is
required in connection with such purchase, Commercial 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 period has
expired or been terminated or such approval has been obtained and any requisite
waiting period shall have passed.  In the event of the failure or refusal of
Commercial to purchase all of the shares covered by the Offeror's Notice or any
applicable regulatory authority shall disapprove Commercial's proposed purchase
of such shares, Wesbanco may sell all, but not less than all, of such shares to
such third party at no less than the price specified and on terms no more
favorable than those set forth in the Offeror's Notice.  The requirements of
this Section 9 shall not apply to any disposition (i) as a result of which the
proposed transferee would own not more than five percent of the then outstanding
shares of Commercial Common Stock, (ii) of Commercial Common Stock by a person
to which Wesbanco has assigned its rights under the Option in accordance with
Section 11(c) hereof or (iii) pursuant to a registration under Section 7 hereof.
<PAGE>
 
     11.  Miscellaneous.

        a.  Expenses.  Except as otherwise 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.

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

        c. Assignment. 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.

        d.  Notices.  All notices or other communications which are required or
     permitted hereunder shall be in writing and sufficient if delivered in the
     manner and to the addresses provided for in or pursuant to Section 17 of
     the Merger Agreement.

        e. Counterparts. This Option Agreement may be executed in any number of
     counterparts, and each such counterpart shall be deemed to be an original
     instrument, but all such counterparts together shall constitute but one
     agreement.

        f.  Specific Performance.  The parties agree that damages would be an
     inadequate remedy for a breach of the provisions of this Option Agreement
     by either party hereto and that this Option Agreement may be enforced by
     either party hereto through injunctive or other equitable relief.

        g.  Governing Law.  This Option Agreement shall be governed by and
     construed in accordance with the laws of the State of West Virginia
     applicable to agreements made and entirely to be performed within such
     state and such federal laws as may be applicable.

     IN WITNESS WHEREOF, each of the parties hereto has executed this Option
Agreement as of the day and year first written above.

                                     WESBANCO, INC.


                                     By  /s/ Edward M. George
                                              Its  President


                                     COMMERCIAL BANCSHARES,
                                     INCORPORATED


                                     By  /s/ Larry G. Johnson
                                               Its Executive Vice President &
                                                Chief Financial Officer