Document:

<PAGE>   1
                                                                     Exhibit 4.4

                  FORM OF EXCHANGE CAPITAL SECURITY CERTIFICATE

                           [FORM OF FACE OF SECURITY]

                  [IF THIS CAPITAL SECURITY IS A GLOBAL CAPITAL SECURITY,
INSERT: THIS CAPITAL SECURITY IS A GLOBAL CAPITAL SECURITY WITHIN THE MEANING OF
THE DECLARATION HEREINAFTER REFERRED TO AND IS REGISTERED IN THE NAME OF THE
DEPOSITORY TRUST COMPANY (THE "CLEARING AGENCY") OR A NOMINEE OF THE CLEARING
AGENCY. THIS CAPITAL SECURITY IS EXCHANGEABLE FOR CAPITAL SECURITIES REGISTERED
IN THE NAME OF A PERSON OTHER THAN THE CLEARING AGENCY OR ITS NOMINEE ONLY IN
THE LIMITED CIRCUMSTANCES DESCRIBED IN THE DECLARATION AND NO TRANSFER OF THIS
CAPITAL SECURITY (OTHER THAN A TRANSFER OF THIS CAPITAL SECURITY AS A WHOLE BY
THE CLEARING AGENCY TO A NOMINEE OF THE CLEARING AGENCY OR BY A NOMINEE OF THE
CLEARING AGENCY TO THE CLEARING AGENCY OR ANOTHER NOMINEE OF THE CLEARING
AGENCY) MAY BE REGISTERED EXCEPT IN LIMITED CIRCUMSTANCES.

                  UNLESS THIS CAPITAL SECURITY IS PRESENTED BY AN AUTHORIZED
REPRESENTATIVE OF THE CLEARING AGENCY TO THE TRUST OR ITS AGENT FOR REGISTRATION
OF TRANSFER, EXCHANGE OR PAYMENT, AND ANY CAPITAL SECURITY ISSUED IS REGISTERED
IN THE NAME OF CEDE & CO. OR SUCH OTHER NAME AS REQUESTED BY AN AUTHORIZED
REPRESENTATIVE OF THE CLEARING AGENCY AND ANY PAYMENT HEREON IS MADE TO CEDE &
CO., ANY TRANSFER, PLEDGE OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO
ANY PERSON IS WRONGFUL SINCE THE REGISTERED OWNER HEREOF, CEDE & CO., HAS AN
INTEREST HEREIN.]

         THE HOLDER OF THIS CAPITAL SECURITY BY ITS ACCEPTANCE HEREOF ALSO
AGREES, REPRESENTS AND WARRANTS THAT IT IS NOT AN EMPLOYEE BENEFIT, INDIVIDUAL
RETIREMENT ACCOUNT OR OTHER PLAN OR ARRANGEMENT SUBJECT TO TITLE I OF THE
EMPLOYEE RETIREMENT INCOME SECURITY ACT OF 1974, AS AMENDED ("ERISA"), OR
SECTION 4975 OF THE INTERNAL REVENUE CODE OF 1986, AS AMENDED (THE "CODE") (EACH
A "PLAN"), OR AN ENTITY WHOSE UNDERLYING ASSETS INCLUDE "PLAN ASSETS" BY REASON
OF ANY PLAN'S INVESTMENT IN THE ENTITY AND NO PERSON INVESTING "PLAN ASSETS" OF
ANY PLAN MAY ACQUIRE OR HOLD THE CAPITAL SECURITIES OR ANY INTEREST THEREIN,
UNLESS SUCH PURCHASER OR HOLDER IS ELIGIBLE FOR THE EXEMPTIVE RELIEF AVAILABLE
UNDER U.S. DEPARTMENT OF LABOR PROHIBITED TRANSACTION CLASS EXEMPTION 96-23,
95-60, 91-38, 90-1 OR 84-14 OR ANOTHER APPLICABLE EXEMPTION OR ITS PURCHASE AND
HOLDING OF CAPITAL SECURITIES IS NOT PROHIBITED BY SECTION 406 OF ERISA OR
SECTION 4975 OF THE CODE WITH RESPECT TO SUCH PURCHASE OR HOLDING. ANY PURCHASER
OR HOLDER OF THE CAPITAL SECURITIES OR ANY INTEREST THEREIN WILL BE DEEMED TO
HAVE REPRESENTED BY ITS PURCHASE AND HOLDING THEREOF THAT EITHER (i) IT IS NOT
AN EMPLOYEE BENEFIT PLAN

<PAGE>   2

WITHIN THE MEANING OF SECTION 3(3) OF ERISA, OR A PLAN TO WHICH SECTION 4975 OF
THE CODE IS APPLICABLE, A TRUSTEE OR OTHER PERSON ACTING ON BEHALF OF AN
EMPLOYEE BENEFIT PLAN OR PLAN, OR ANY OTHER PERSON OR ENTITY USING THE ASSETS OF
ANY EMPLOYEE BENEFIT PLAN OR PLAN TO FINANCE SUCH PURCHASE, OR (ii) SUCH
PURCHASE WILL NOT RESULT IN A PROHIBITED TRANSACTION UNDER SECTION 406 OF ERISA
OR SECTION 4975 OF THE CODE FOR WHICH THERE IS NO APPLICABLE STATUTORY OR
ADMINISTRATIVE EXEMPTION.

         THE CAPITAL SECURITIES WILL BE ISSUED AND MAY BE TRANSFERRED ONLY IN
BLOCKS HAVING A LIQUIDATION AMOUNT OF NOT LESS THAN $100,000 (100 CAPITAL
SECURITIES) AND MULTIPLES OF $1,000 IN EXCESS THEREOF. ANY ATTEMPTED TRANSFER OF
CAPITAL SECURITIES IN A BLOCK HAVING A LIQUIDATION AMOUNT OF LESS THAN $100,000
(100 CAPITAL SECURITIES) SHALL BE DEEMED TO BE VOID AND OF NO LEGAL EFFECT
WHATSOEVER. ANY SUCH PURPORTED TRANSFEREE SHALL BE DEEMED NOT TO BE THE HOLDER
OF SUCH CAPITAL SECURITIES FOR ANY PURPOSE, INCLUDING, BUT NOT LIMITED TO, THE
RECEIPT OF DISTRIBUTIONS ON SUCH CAPITAL SECURITIES, AND SUCH PURPORTED
TRANSFEREE SHALL BE DEEMED TO HAVE NO INTEREST WHATSOEVER IN SUCH CAPITAL
SECURITIES.

                                      -2-
<PAGE>   3

Certificate Number: [________________________]   Aggregate Liquidation Amount:
                                               $
CUSIP Number:[_____________]

                    Certificate Evidencing Capital Securities

                                       of

                              BFOH Capital Trust I

                       9.875% Capital Securities, Series B
                (liquidation amount $1,000 per Capital Security)

                  BFOH Capital Trust I, a statutory business trust created under
the laws of the State of Delaware (the "Trust"), hereby certifies that [ ] (the
"Holder") is the registered owner of $ in aggregate liquidation amount of
Capital Securities of the Trust](1) [the aggregate liquidation amount of Capital
Securities of the Trust specified in Schedule A hereto](2) representing
undivided preferred beneficial interests in the assets of the Trust designated
the 9.875% Capital Securities, Series B (liquidation amount $1,000 per Capital
Security) (the "Capital Securities"). The Capital Securities are transferable on
the books and records of the Trust, in person or by a duly authorized attorney,
upon surrender of this certificate duly endorsed and in proper form for
transfer. The designation, rights, privileges, restrictions, preferences and
other terms and provisions of the Capital Securities represented hereby are
issued and shall in all respects be subject to the provisions of the Amended and
Restated Declaration of the Trust, dated as of October 18, 1999, as the same may
be amended from time to time (the "Declaration"), including the designation of
the terms of the Capital Securities as set forth in Annex I to the Declaration.
Capitalized terms used but not defined herein shall have the meaning given them
in the Declaration. The Sponsor will provide a copy of the Declaration, the
Capital Securities Guarantee and the Indenture (including any supplemental
indenture) to a Holder without charge upon written request to the Trust at its
principal place of business.

                  Upon receipt of this Certificate, the Holder is bound by the
Declaration and is entitled to the benefits thereunder and to the benefits of
the Capital Securities Guarantee to the extent provided therein.

                  By acceptance hereof, the Holder agrees, for United States
federal income tax purposes, to treat the Debentures as indebtedness and the
Capital Securities as evidence of indirect beneficial ownership in the
Debentures.

--------------------
(1)      Insert in Definitive Capital Securities only.

(2)      Insert in Global Capital Securities only.

                                      -3-
<PAGE>   4

         IN WITNESS WHEREOF, the Trust has executed this certificate this
[_______] day of [____________________].

                                        BFOH CAPITAL TRUST I

                                        By:
                                            Name:
                                            Administrative Trustee

                PROPERTY TRUSTEE'S CERTIFICATE OF AUTHENTICATION

         This is one of the 9.875% Capital Securities, Series B of BFOH Capital
Trust I referred to in the within-mentioned Declaration.

Dated:________________, _____

                                      WILMINGTON TRUST COMPANY,
                                      not in its individual capacity but solely
                                      as Property Trustee

                                      By:
                                          Authorized Signatory

                                      -4-
<PAGE>   5

                          [FORM OF REVERSE OF SECURITY]

                  Distributions on each Capital Security will be payable at a
fixed rate per annum of 9.875% (the "Coupon Rate") of the liquidation amount of
$1000 per Capital Security, such rate being the rate of interest payable on the
Debentures to be held by the Property Trustee. Distributions in arrears for more
than one semi-annual period will bear interest thereon compounded semi-annually
at the Coupon Rate (to the extent permitted by applicable law). The term
"Distributions," as used herein, includes such cash distributions and any and
all such interest, if any, payable unless otherwise stated. A Distribution is
payable only to the extent that payments are made in respect of the Debentures
held by the Property Trustee and to the extent the Property Trustee has funds
legally available therefor.

                  Distributions on the Capital Securities will be cumulative,
will accumulate from the most recent date to which Distributions have been paid
or, if no Distributions have been paid, from October 18, 1999 and will be
payable semi-annually in arrears, on April 15 and October 15 of each year,
commencing April 15, 2000, except as otherwise described below. Distributions
will be computed on the basis of a 360-day year of twelve 30-day months. As long
as no Event of Default has occurred and is continuing under the Indenture, the
Debenture Issuer has the right under the Indenture to defer payments of interest
by extending the interest payment period at any time and from time to time on
the Debentures for a period not exceeding 10 consecutive semi-annual calendar
periods, including the first such semi-annual period during such extension
period (each an "Extension Period"), provided that no Extension Period shall end
on a date other than an Interest Payment Date for the Debentures or extend
beyond the Maturity Date of the Debentures. As a consequence of such deferral,
Distributions (other than Liquidated Damages, if any) will also be deferred.
Notwithstanding such deferral, semi-annual Distributions will continue to
accumulate with interest thereon (to the extent permitted by applicable law, but
not at a rate exceeding the rate of interest then accruing on the Debentures) at
the Coupon Rate compounded semi-annually during any such Extension Period. Prior
to the termination of any Extension Period, the Debenture Issuer may further
defer payments of interest by further extending such Extension Period; provided
that such Extension Period, together with all such previous and further
extensions within such Extension Period, may not (i) exceed 10 consecutive
semi-annual periods, including the first semi-annual period during such
Extension Period, (ii) end on a date other than an Interest Payment Date for the
Debentures or (iii) extend beyond the Maturity Date of the Debentures. Payments
of accumulated Distributions will be payable to Holders as they appear on the
books and records of the Trust on the record date immediately preceding the end
of the Extension Period. Upon the termination of any Extension Period and the
payment of all amounts then due, the Debenture Issuer may commence a new
Extension Period, subject to the above requirements.

                  Subject to receipt by the Sponsor of any and all required
regulatory approvals and to certain other conditions set forth in the
Declaration and the Indenture, the Property Trustee may, at the direction of the
Sponsor, at any time dissolve the Trust and after satisfaction of liabilities to
creditors of the Trust as provided by applicable law, cause the Debentures to be
distributed to the Holders of the Securities in liquidation of the Trust or,
simultaneously with any redemption of the Debentures, cause a Like Amount of the
Securities to be redeemed by the Trust.

                  The Capital Securities shall be redeemable as provided in the
Declaration.

<PAGE>   6

                                   ASSIGNMENT

FOR VALUE RECEIVED, the undersigned hereby assigns and transfers this Capital
Security Certificate to:

            (Assignee's social security or tax identification number)

                       (Address and zip code of assignee)

and irrevocably appoints

                                                                   agent
to transfer this Capital Security Certificate on the books of the Trust.
The agent may substitute another to act for him or her.

Date:
     ---------------
Signature:
          ---------------------------

(Sign exactly as your name appears on the other side of this Capital Security
Certificate)

Signature Guarantee:
                    ------------------------

-----------------------
         Signature must be guaranteed by an "eligible guarantor institution"
         that is a bank, stockbroker, savings and loan association or credit
         union meeting the requirements of the Registrar, which requirements
         include membership or participation in the Securities Transfer Agents
         Medallion Program ("STAMP") or such other "signature guarantee program"
         as may be determined by the Registrar in addition to, or in
         substitution for, STAMP, all in accordance with the Securities Exchange
         Act of 1934, as amended.<PAGE>   1
                                                                     Exhibit 4.5

               ===================================================

                 SERIES A CAPITAL SECURITIES GUARANTEE AGREEMENT

                              BANCFIRST OHIO CORP.

                          Dated as of October 18, 1999

               ===================================================

<PAGE>   2

                                TABLE OF CONTENTS
                                -----------------

                                                                     Page
                                                                     ----

                                    ARTICLE I

                         DEFINITIONS AND INTERPRETATION

SECTION 1.1  Definitions and Interpretation ...........................2

                              ARTICLE II

                          TRUST INDENTURE ACT

SECTION 2.1  Trust Indenture Act; Application .........................5
SECTION 2.2  Lists of Holders of Securities ...........................5
SECTION 2.3  Reports by the Capital Securities Guarantee Trustee ......6
SECTION 2.4  Periodic Reports .........................................6
SECTION 2.5  Evidence of Compliance with Conditions Precedent .........6
SECTION 2.6  Waiver of Events of Default ..............................6
SECTION 2.7  Notice of Events of Default ..............................6
SECTION 2.8  Conflicting Interests ....................................7

                              ARTICLE III

                     POWERS, DUTIES AND RIGHTS OF
                 CAPITAL SECURITIES GUARANTEE TRUSTEE

SECTION 3.1  Powers and Duties of the Capital Securities
             Guarantee Trustee ........................................7
SECTION 3.2  Certain Rights of Capital Securities Guarantee
             Trustee ..................................................9
SECTION 3.3  Not Responsible for Recitals or Issuance of Series
             A Capital Securities Guarantee ..........................10

                              ARTICLE IV

                 CAPITAL SECURITIES GUARANTEE TRUSTEE

SECTION 4.1  Capital Securities Guarantee Trustee; Eligibility .......11
SECTION 4.2  Appointment, Removal and Resignation of Capital
             Securities Guarantee Trustee ............................11

                               ARTICLE V

                               GUARANTEE

SECTION 5.1  Guarantee ...............................................12
SECTION 5.2  Waiver of Notice and Demand .............................12
SECTION 5.3  Obligations Not Affected ................................12
SECTION 5.4  Rights of Holders .......................................13

                                 (i)
<PAGE>   3

                                                                     Page
                                                                     ----

SECTION 5.5  Guarantee of Payment ....................................14
SECTION 5.6  Subrogation .............................................14
SECTION 5.7  Independent Obligations .................................14

                              ARTICLE VI

               LIMITATION OF TRANSACTIONS; SUBORDINATION

SECTION 6.1  Limitation of Transactions ..............................14
SECTION 6.2  Ranking .................................................15

                              ARTICLE VII

                              TERMINATION

SECTION 7.1  Termination .............................................15

                             ARTICLE VIII

                            INDEMNIFICATION

SECTION 8.1  Exculpation .............................................16
SECTION 8.2  Compensation and Indemnification ........................16

                              ARTICLE IX

                             MISCELLANEOUS

SECTION 9.1  Successors and Assigns ..................................17
SECTION 9.2  Amendments ..............................................17
SECTION 9.3  Notices .................................................17
SECTION 9.4  Exchange Offer ..........................................18
SECTION 9.5  Benefit .................................................18
SECTION 9.6  Governing Law ...........................................19

                                      (ii)
<PAGE>   4

                              CROSS REFERENCE TABLE

SECTION OF TRUST
INDENTURE ACT OF                                         SECTION OF GUARANTEE
1939, AS AMENDED                                               AGREEMENT
----------------                                         ---------------------

    310(a)     ............................................      4.1(a)
    310(b)     ............................................    4.1(c), 2.8
    310(c)     ............................................      N/A
    311(a)     ............................................      2.2(b)
    311(b)     ............................................      2.2(b)
    311(c)     ............................................      N/A
    312(a)     ............................................      2.2(a)
    312(b)     ............................................      2.2(b)
     313       ............................................      2.3
    314(a)     ............................................      2.4
    314(b)     ............................................      N/A
    314(c)     ............................................      2.5
    314(d)     ............................................      N/A
    314(e)     ............................................   1.1, 2.5, 3.2
    314(f)     ............................................     2.1, 3.2
    315(a)     ............................................      3.1(d)
    315(b)     ............................................      2.7
    315(c)     ............................................      3.1(c)
    315(d)     ............................................      3.1(d)
    316(a)     ............................................   1.1, 2.6, 5.4
    316(b)     ............................................      5.3
    316(c)     ............................................      9.2
    317(a)     ............................................      N/A
    317(b)     ............................................      N/A
    318(a)     ............................................      2.1(a)
    318(b)     ............................................      2.1(b)
    318(c)     ............................................      2.1(b)

---------------------------

*    This Cross-Reference Table does not constitute part of this Guarantee
     Agreement and shall not affect the interpretation of any of its terms or
     provisions.

                                     (iii)

<PAGE>   5

                 SERIES A CAPITAL SECURITIES GUARANTEE AGREEMENT

         This SERIES A CAPITAL SECURITIES GUARANTEE AGREEMENT (the "Series A
Capital Securities Guarantee"), dated as of October 18, 1999, is executed and
delivered by BANCFIRST OHIO CORP., an Ohio corporation (the "Guarantor"), and
WILMINGTON TRUST COMPANY, a Delaware banking corporation, as trustee (the
"Capital Securities Guarantee Trustee" or "Trustee"), for the benefit of the
Holders (as defined herein) from time to time of the Series A Capital Securities
(as defined herein) of BFOH CAPITAL TRUST I, a Delaware statutory business trust
(the "Issuer").

         WHEREAS, pursuant to an Amended and Restated Declaration of Trust (the
"Declaration"), dated as of October 18, 1999, by and among the trustees of the
Issuer named therein, the Guarantor, as sponsor, and the Holders from time to
time of undivided beneficial interests in the assets of the Issuer, the Issuer
(i) is issuing on the date hereof 20,000 capital securities, having an aggregate
liquidation amount of $20,000,000, such capital securities being designated the
9.875% Capital Securities, Series A (collectively the "Series A Capital
Securities") and (ii) in connection with an Exchange Offer (as defined in the
Declaration), will execute and deliver the Series B Capital Securities Guarantee
(as defined in the Declaration) for the benefit of Holders of the Series B
Capital Securities (as defined in the Declaration).

         WHEREAS, as incentive for the Holders to purchase the Series A Capital
Securities, the Guarantor desires irrevocably and unconditionally to agree, to
the extent set forth in this Series A Capital Securities Guarantee, to pay the
Guarantee Payments (as defined herein) to the Holders of the Series A Capital
Securities, and the Guarantor agrees to make certain other payments on the terms
and conditions set forth herein.

         WHEREAS, the Guarantor is also executing and delivering the Common
Securities Guarantee Agreement, dated as of October 18, 1999 (the "Common
Securities Guarantee"), for the benefit of the holders of the Common Securities
(as defined herein), the terms of which provide that if an Event of Default (as
defined in the Declaration) has occurred and is continuing, the rights of
holders of the Common Securities to receive Guarantee Payments under the Common
Securities Guarantee are subordinated, to the extent and in the manner set forth
in the Common Securities Guarantee, to the rights of Holders of Series A Capital
Securities and the Series B Capital Securities to receive Guarantee Payments
under this Series A Capital Securities Guarantee and the Series B Capital
Securities Guarantee, as the case may be.

         NOW, THEREFORE, in consideration of the purchase by each Holder of the
Series A Capital Securities, which purchase the Guarantor hereby acknowledges
shall benefit the Guarantor, the Guarantor executes and delivers this Series A
Capital Securities Guarantee for the benefit of such Holders.

<PAGE>   6

                                    ARTICLE I

                         DEFINITIONS AND INTERPRETATION

     SECTION 1.1    DEFINITIONS AND INTERPRETATION

     In this Series A Capital Securities Guarantee, unless the context otherwise
requires:

     (a)  capitalized terms used in this Series A Capital Securities Guarantee
but not defined in the preamble above have the respective meanings assigned to
them in this Section 1.1;

     (b)  terms defined in the Declaration as in effect at the date of execution
of this Series A Capital Securities Guarantee have the same meaning when used in
this Series A Capital Securities Guarantee unless otherwise defined in this
Series A Capital Securities Guarantee,

     (c)  a term defined anywhere in this Series A Capital Securities Guarantee
has the same meaning throughout;

     (d)  all references to "the Series A Capital Securities Guarantee" or "this
Series A Capital Securities Guarantee" are references to this Series A Capital
Securities Guarantee as modified, supplemented or amended from time to time;

     (e)  all references in this Series A Capital Securities Guarantee to
Articles and Sections are references to Articles and Sections of this Series A
Capital Securities Guarantee, unless otherwise specified;

     (f)  a term defined in the Trust Indenture Act has the same meaning when
used in this Series A Capital Securities Guarantee, unless otherwise defined in
this Series A Capital Securities Guarantee or unless the context otherwise
requires; and

     (g)  a reference to the singular includes the plural and vice versa.

     "AFFILIATE" has the same meaning as given to that term in Rule 405 under
the Securities Act of 1933, as amended, or any successor rule thereunder.

     "BUSINESS DAY" shall mean any day other than a Saturday or a Sunday, or a
day on which banking institutions in New York, New York or Wilmington, Delaware
are authorized or required by law or executive order to remain closed.

     "CAPITAL SECURITIES GUARANTEE TRUSTEE" shall mean Wilmington Trust Company,
as Trustee under the Series A Capital Securities Guarantee, until a Successor
Capital Securities Guarantee Trustee has been appointed and has accepted such
appointment pursuant to the terms of this Series A Capital Securities Guarantee
and thereafter means each such Successor Capital Securities Guarantee Trustee.

     "COMMON SECURITIES" shall mean the securities representing common undivided
beneficial interests in the assets of the Issuer.

                                      -2-
<PAGE>   7

     "CORPORATE TRUST OFFICE" shall mean the office of the Capital Securities
Guarantee Trustee at which the corporate trust business of the Capital
Securities Guarantee Trustee shall, at any particular time, be principally
administered, which office at the date of execution of this Agreement is located
at Rodney Square North, 1100 North Market Street, Wilmington, Delaware
19890-0001, Attention: Corporate Trust Administration.

     "COVERED PERSON" shall mean any Holder or beneficial owner of Series A
Capital Securities.

     "DEBENTURES" shall mean the series of subordinated debt securities of
the Guarantor designated the 9.875% Junior Subordinated Deferrable Interest
Debentures due October 15, 2029, Series A, held by the Property Trustee (as
defined in the Declaration) of the Issuer.

     "EVENT OF DEFAULT" shall mean a default by the Guarantor on any of its
payment or other obligations under this Series A Capital Securities Guarantee;
PROVIDED, HOWEVER, that, except with respect to default in respect of any
Guarantee Payment, no default by the Guarantor hereunder shall constitute an
Event of Default unless the Guarantor shall have received written notice of the
default and shall not have cured such default within 60 days after receipt
thereof.

     "GUARANTEE PAYMENTS" shall mean the following payments or distributions,
without duplication, with respect to the Series A Capital Securities, to the
extent not paid or made by or on behalf of the Issuer: (i) any accumulated and
unpaid Distributions (as defined in the Declaration) that are required to be
paid on such Series A Capital Securities, to the extent the Issuer has funds
legally available therefor at such time, (ii) the redemption price, including
all accumulated and unpaid Distributions to the date of redemption (the
"Redemption Price"), to the extent the Issuer has funds legally available
therefor at such time, with respect to any Series A Capital Securities called
for redemption, and (iii) upon a voluntary or involuntary dissolution, winding
up or liquidation of the Issuer (other than in connection with the distribution
of Debentures to the Holders in exchange for Series A Capital Securities or in
connection with the redemption of the Series A Capital Securities, in each case
as provided in the Declaration), the lesser of (a) the aggregate of the
liquidation amount and all accumulated and unpaid Distributions on the Series A
Capital Securities to the date of payment, to the extent the Issuer has funds
legally available therefor at such time, and (b) the amount of assets of the
Issuer remaining available for distribution to Holders after satisfaction of
liabilities to creditors of the Issuer as required by applicable law (in either
case, the "Liquidation Distribution"). If an Event of Default has occurred and
is continuing, no Guarantee Payments under the Common Securities Guarantee with
respect to the Common Securities or any guarantee payment under the Common
Securities Guarantee or any Other Common Securities Guarantee shall be made
until the Holders of the Series A Capital Securities shall be paid in full the
Guarantee Payments to which they are entitled under this Series A Capital
Securities Guarantee.

     "HOLDER" shall mean any holder, as registered on the books and records of
the Issuer, of any Series A Capital Securities; PROVIDED, HOWEVER, that, in
determining whether the holders of the requisite percentage of Series A Capital
Securities have given any request, notice, consent or waiver hereunder, "Holder"
shall not include the Guarantor or any Person actually known to a Responsible
Officer of the Capital Securities Guarantee Trustee to be an Affiliate of the
Guarantor.

     "INDEMNIFIED PERSON" shall mean the Capital Securities Guarantee Trustee
(including in its individual capacity), any Affiliate of the Capital Securities
Guarantee Trustee, or any officers, directors, shareholders, members, partners,
employees, representatives, nominees, custodians or agents of the Capital
Securities Guarantee Trustee.

                                      -3-
<PAGE>   8

     "INDENTURE" shall mean the Indenture, dated as of October 18, 1999, between
BancFirst Ohio Corp., as issuer of Debentures (the "Debenture Issuer"), and
Wilmington Trust Company, as trustee, pursuant to which the Debentures are to be
issued to the Property Trustee of the Issuer.

     "MAJORITY IN LIQUIDATION AMOUNT OF THE SERIES A CAPITAL SECURITIES" shall
mean, except as provided by the Trust Indenture Act, a vote by Holder(s) of the
Series A Capital Securities, voting separately as a class, of more than 50% of
the aggregate liquidation amount (including the amount that would be paid on
redemption, liquidation or otherwise, plus accumulated and unpaid Distributions
to the date upon which the voting percentages are determined) of all outstanding
Series A Capital Securities, excluding Series A Capital Securities held by the
Guarantor, the Issuer or any Affiliate thereof.

     "OFFICERS' CERTIFICATE" shall mean, with respect to any Person, a
certificate signed by the Chairman, the Chief Executive Officer, the President,
an Executive or Senior Vice President, a Vice President, the Chief Financial
Officer and the Secretary or an Assistant Secretary. Any Officers' Certificate
delivered with respect to compliance with a condition or covenant provided for
in this Series A Capital Securities Guarantee shall include:

     (a)  a statement that each officer signing the Officers' Certificate has
read the covenants or conditions and the definitions relating thereto;

     (b)  a statement that each such officer has made such examination or
investigation as, in such officer's opinion, is necessary to enable such officer
to express an informed opinion as to whether or not such covenant or condition
has been complied with; and

     (c)  a statement as to whether or not, in the opinion of each such officer,
such condition or covenant has been complied with.

     "OTHER COMMON SECURITIES GUARANTEES" shall have the same meaning as "Other
Guarantees" in the Common Securities Guarantee.

     "OTHER DEBENTURES" shall mean all junior subordinated debentures, other
than the Debentures and the Series B Debentures (as defined in the Indenture),
issued by the Guarantor, from time to time and sold to trusts other than the
Issuer to be established by the Guarantor (if any), in each case similar to the
Issuer.

     "OTHER GUARANTEES" shall mean all guarantees, other than this Series A
Capital Securities Guarantee and the Series B Capital Securities Guarantee, to
be issued by the Guarantor with respect to capital securities (if any) similar
to the Series A Capital Securities, issued by trusts other than the Issuer to be
established by the Guarantor (if any), in each case similar to the Issuer.

     "PERSON" shall mean a legal person, including any individual, corporation,
estate, partnership, joint venture, association, joint stock company, limited
liability company, trust, unincorporated association, or government or any
agency or political subdivision thereof, or any other entity of whatever nature.

     "REGISTRATION RIGHTS AGREEMENT" shall mean the Registration Rights
Agreement, dated as of October 18, 1999, by and among the Guarantor, the Issuer
and the Initial Purchaser named therein, as such agreement may be amended,
modified or supplemented from time to time.

                                      -4-
<PAGE>   9

     "RESPONSIBLE OFFICER" shall mean, with respect to a Person, any officer
with direct responsibility for the administration of any matters relating to
this Series A Capital Securities Guarantee.

     "SUCCESSOR CAPITAL SECURITIES GUARANTEE TRUSTEE" shall mean a successor
Capital Securities Guarantee Trustee possessing the qualifications to act as
Capital Securities Guarantee Trustee under Section 4.1.

     "TRUST INDENTURE ACT" shall mean the Trust Indenture Act of 1939, as
amended.

     "TRUST SECURITIES" shall mean the Common Securities and the Series A
Capital Securities and Series B Capital Securities, collectively.

                                   ARTICLE II

                               TRUST INDENTURE ACT

     SECTION 2.1    TRUST INDENTURE ACT; APPLICATION

     (a)  This Series A Capital Securities Guarantee is subject to the
provisions of the Trust Indenture Act that are required to be part of this
Series A Capital Securities Guarantee and shall, to the extent applicable, be
governed by such provisions.

     (b)  If and to the extent that any provision of this Series A Capital
Securities Guarantee limits, qualifies or conflicts with the duties imposed by
Section 310 to 317, inclusive, of the Trust Indenture Act, such imposed duties
shall control. If any provision of this Series A Capital Securities Guarantee
modifies or excludes any provision of the Trust Indenture Act that may be so
modified or excluded, the modified or excluded provision of the Trust Indenture
Act shall be deemed to apply to this Series A Capital Securities Guarantee as so
modified or excluded, as the case may be.

     SECTION 2.2    LISTS OF HOLDERS OF SECURITIES

     (a)  The Guarantor shall provide the Capital Securities Guarantee Trustee
(unless the Capital Securities Guarantee Trustee is otherwise the registrar of
the Series A Capital Securities) with a list, in such form as the Capital
Securities Guarantee Trustee may reasonably require, of the names and addresses
of the Holders of the Series A Capital Securities ("List of Holders") as of such
date, (i) within fourteen (14) days after each record date for payment of
Distributions (as defined in the Declaration), and (ii) at any other time within
30 days of receipt by the Guarantor of a written request for a List of Holders
as of a date no more than 14 days before such List of Holders is given to the
Capital Securities Guarantee Trustee; PROVIDED, HOWEVER, that the Guarantor
shall not be obligated to provide such List of Holders at any time the List of
Holders does not differ from the most recent List of Holders given to the
Capital Securities Guarantee Trustee by the Guarantor. The Capital Securities
Guarantee Trustee may destroy any List of Holders previously given to it upon
receipt of a new List of Holders.

     (b)  The Capital Securities Guarantee Trustee shall comply with its
obligations under Sections 31l(a), 31l(b) and Section 312(b) of the Trust
Indenture Act.

                                      -5-
<PAGE>   10

     SECTION 2.3    REPORTS BY THE CAPITAL SECURITIES GUARANTEE TRUSTEE

     Within 60 days after the date hereof, and no later than the anniversary
date hereof in each succeeding year, the Capital Securities Guarantee Trustee
shall provide to the Holders of the Series A Capital Securities such reports as
are required by Section 313 of the Trust Indenture Act, if any, in the form and
in the manner provided by Section 313 of the Trust Indenture Act. The Capital
Securities Guarantee Trustee shall also comply with the requirements of Section
313(d) of the Trust Indenture Act.

     SECTION 2.4    PERIODIC REPORTS

     The Guarantor shall provide to the Capital Securities Guarantee Trustee
such documents, reports and information as are required by Section 314 (if any)
and the compliance certificate required by Section 314 of the Trust Indenture
Act in the form, in the manner and at the times required by Section 314 of the
Trust Indenture Act. Delivery of such reports, information and documents to the
Capital Securities Guarantee Trustee is for informational purposes only and the
Capital Securities Guarantee Trustee's receipt of such shall not constitute
constructive notice of any information contained therein or determinable from
information contained therein, including the Guarantor's compliance with any of
its covenants hereunder (as to which the Capital Securities Guarantee Trustee is
entitled to rely exclusively on Officers' Certificates).

     SECTION 2.5    EVIDENCE OF COMPLIANCE WITH CONDITIONS PRECEDENT

     The Guarantor shall provide to the Capital Securities Guarantee Trustee
such evidence of compliance with the conditions precedent, if any, provided for
in this Series A Capital Securities Guarantee that relate to any of the matters
set forth in Section 314(c) of the Trust Indenture Act. Any certificate or
opinion required to be given by an officer pursuant to Section 314(c)(1) may be
given in the form of an Officers' Certificate.

     SECTION 2.6    WAIVER OF EVENTS OF DEFAULT

     The Holders of a Majority in Liquidation Amount of the Series A Capital
Securities may, by vote, on behalf of the Holders of all of the Series A Capital
Securities, waive any past Event of Default and its consequences. Upon such
waiver, any such Event of Default shall cease to exist, and any Event of Default
arising therefrom shall be deemed to have been cured, for every purpose of this
Series A Capital Securities Guarantee, but no such waiver shall extend to any
subsequent or other default or Event of Default or impair any right consequent
thereon.

     SECTION 2.7    NOTICE OF EVENTS OF DEFAULT

     (a)  The Capital Securities Guarantee Trustee shall, within 10 Business
Days after the occurrence of an Event of Default with respect to this Series A
Capital Securities Guarantee actually known to a Responsible Officer of the
Capital Securities Guarantee Trustee, transmit by mail, first class postage
prepaid, to all Holders of the Series A Capital Securities, notices of all such
Events of Default, unless such Events of Default have been cured before the
giving of such notice; PROVIDED, HOWEVER, that, except in the case of an Event
of Default arising from the non-payment of any Guarantee Payment, the Capital
Securities Guarantee Trustee shall be protected in withholding such notice if
and so long as a Responsible Officer of the Capital Securities Guarantee Trustee
in good

                                      -6-
<PAGE>   11

faith determines that the withholding of such notice is in the interests of the
Holders of the Series A Capital Securities.

     (b)  The Capital Securities Guarantee Trustee shall not be deemed to have
knowledge of any Event of Default unless the Capital Securities Guarantee
Trustee shall have received written notice, or a Responsible Officer of the
Capital Securities Guarantee Trustee charged with the administration of the
Declaration shall have obtained actual knowledge, of such Event of Default.

     SECTION 2.8    CONFLICTING INTERESTS

     The Declaration shall be deemed to be specifically described in this Series
A Capital Securities Guarantee for the purposes of clause (i) of the first
proviso contained in Section 310(b) of the Trust Indenture Act.

                                   ARTICLE III

                          POWERS, DUTIES AND RIGHTS OF
                      CAPITAL SECURITIES GUARANTEE TRUSTEE

     SECTION 3.1    POWERS AND DUTIES OF THE CAPITAL SECURITIES GUARANTEE
                    TRUSTEE

     (a)  This Series A Capital Securities Guarantee shall be held by the
Capital Securities Guarantee Trustee for the benefit of the Holders of the
Series A Capital Securities, and the Capital Securities Guarantee Trustee shall
not transfer this Series A Capital Securities Guarantee to any Person except a
Holder of the Series A Capital Securities exercising his or her rights pursuant
to Section 5.4(b) or to a Successor Capital Securities Guarantee Trustee on
acceptance by such Successor Capital Securities Guarantee Trustee of its
appointment to act as Successor Capital Securities Guarantee Trustee. The right,
title and interest of the Capital Securities Guarantee Trustee shall
automatically vest in any Successor Capital Securities Guarantee Trustee, and
such vesting and succession of title shall be effective whether or not
conveyancing documents have been executed and delivered pursuant to the
appointment of such Successor Capital Securities Guarantee Trustee.

     (b)  If an Event of Default actually known to a Responsible Officer of the
Capital Securities Guarantee Trustee has occurred and is continuing, the Capital
Securities Guarantee Trustee shall enforce this Series A Capital Securities
Guarantee for the benefit of the Holders of the Series A Capital Securities.

     (c)  The Capital Securities Guarantee Trustee, before the occurrence of
any Event of Default (of which, other than a default in respect of any Guarantee
Payment, a Responsible Officer of the Property Trustee has actual knowledge) and
after the curing of all such Events of Default that may have occurred, shall
undertake to perform only such duties as are specifically set forth in this
Series A Capital Securities Guarantee, and no implied covenants or obligations
shall be read into this Series A Capital Securities Guarantee against the
Capital Securities Guarantee Trustee. In case an Event of Default has occurred
(that has not been cured or waived pursuant to Section 2.6) and is actually
known to a Responsible Officer of the Capital Securities Guarantee Trustee, the
Capital Securities Guarantee Trustee shall exercise such of the rights and
powers vested in it by this Series A Capital Securities Guarantee, and use the
same degree of care and skill in its exercise thereof, as

                                      -7-
<PAGE>   12

a prudent person would exercise or use under the circumstances in the conduct of
his or her own affairs.

     (d)  No provision of this Series A Capital Securities Guarantee shall be
construed to relieve the Capital Securities Guarantee Trustee from liability for
its own negligent action, its own negligent failure to act, or its own willful
misconduct, except that:

          (i) prior to the occurrence of any Event of Default (of which, other
     than a default in respect of any Guarantee Payment, a Responsible Officer
     of the Property Trustee has actual knowledge) and after the curing or
     waiving of all such Events of Default that may have occurred:

          (A) the duties and obligations of the Capital Securities Guarantee
     Trustee shall be determined solely by the express provisions of this Series
     A Capital Securities Guarantee, and the Capital Securities Guarantee
     Trustee shall not be liable except for the performance of such duties and
     obligations as are specifically set forth in this Series A Capital
     Securities Guarantee, and no implied covenants or obligations shall be read
     into this Series A Capital Securities Guarantee against the Capital
     Securities Guarantee Trustee; and

          (B) in the absence of bad faith on the part of the Capital Securities
     Guarantee Trustee, the Capital Securities Guarantee Trustee may
     conclusively rely, as to the truth of the statements and the correctness of
     the opinions expressed therein, upon any certificates or opinions furnished
     to the Capital Securities Guarantee Trustee and conforming to the
     requirements of this Series A Capital Securities Guarantee; PROVIDED,
     HOWEVER, that in the case of any such certificates or opinions that by any
     provision hereof are specifically required to be furnished to the Capital
     Securities Guarantee Trustee, the Capital Securities Guarantee Trustee
     shall be under a duty to examine the same to determine whether or not on
     their face they conform to the requirements of this Series A Capital
     Securities Guarantee;

          (ii) the Capital Securities Guarantee Trustee shall not be liable for
     any errors of judgment made in good faith by a Responsible Officer of the
     Capital Securities Guarantee Trustee, unless it shall be proved that the
     Capital Securities Guarantee Trustee or such Responsible Officer was
     negligent in ascertaining the pertinent facts upon which such judgment was
     made;

          (iii) the Capital Securities Guarantee Trustee shall not be liable
     with respect to any actions taken or omitted to be taken by it in good
     faith in accordance with the direction of the Holders of a Majority in
     Liquidation Amount of the Series A Capital Securities relating to the time,
     method and place of conducting any proceeding for any remedy available to
     the Capital Securities Guarantee Trustee, or exercising any trust or power
     conferred upon the Capital Securities Guarantee Trustee under this Series A
     Capital Securities Guarantee; and

          (iv) no provision of this Series A Capital Securities Guarantee shall
     require the Capital Securities Guarantee Trustee to expend or risk its own
     funds or otherwise incur personal financial liability in the performance of
     any of its duties or in the exercise of any of its rights or powers, if the
     Capital Securities Guarantee Trustee shall have reasonable grounds for
     believing that the repayment of such funds or liability is not reasonably

                                      -8-
<PAGE>   13

     assured to it under the terms of this Series A Capital Securities Guarantee
     or indemnity, reasonably satisfactory to the Capital Securities Guarantee
     Trustee, against such risk or liability is not reasonably assured to it.

     SECTION 3.2    CERTAIN RIGHTS OF CAPITAL SECURITIES GUARANTEE TRUSTEE

     (a)  Subject to the provisions of Section 3.1:

          (i) the Capital Securities Guarantee Trustee may conclusively rely,
     and shall be fully protected in acting or refraining from acting, upon any
     resolution, certificate, statement, instrument, opinion, report, notice,
     request, direction, consent, order, bond, debenture, note, other evidence
     of indebtedness or other paper or document believed by it to be genuine and
     to have been signed, sent or presented by the proper party or parties;

          (ii) any direction or act of the Guarantor contemplated by this Series
     A Capital Securities Guarantee may be sufficiently evidenced by an
     Officers' Certificate;

          (iii) whenever, in the administration of this Series A Capital
     Securities Guarantee, the Capital Securities Guarantee Trustee shall deem
     it desirable that a matter be proved or established before taking,
     suffering or omitting any action hereunder, the Capital Securities
     Guarantee Trustee (unless other evidence is herein specifically prescribed)
     may, in the absence of bad faith on its part, request and conclusively rely
     upon an Officers' Certificate, which, upon receipt of such request, shall
     be promptly delivered by the Guarantor;

          (iv) the Capital Securities Guarantee Trustee shall have no duty to
     see to any recording, filing or registration of any instrument or other
     document (or any rerecording, refiling or registration thereof);

          (v) the Capital Securities Guarantee Trustee may consult with counsel
     of its selection, and the advice or opinion of such counsel with respect to
     legal matters shall be full and complete authorization and protection in
     respect of any action taken, suffered or omitted by it hereunder in good
     faith and in accordance with such advice or opinion; and such counsel may
     be counsel to the Guarantor or any of its Affiliates and may include any of
     its employees; and the Capital Securities Guarantee Trustee shall have the
     right at any time to seek instructions concerning the administration of
     this Series A Capital Securities Guarantee from any court of competent
     jurisdiction;

          (vi) the Capital Securities Guarantee Trustee shall be under no
     obligation to exercise any of the rights or powers vested in it by this
     Series A Capital Securities Guarantee at the request or direction of any
     Holder, unless such Holder shall have provided to the Capital Securities
     Guarantee Trustee such security and indemnity, reasonably satisfactory to
     the Capital Securities Guarantee Trustee, against the costs, expenses
     (including attorneys' fees and expenses and the expenses of the Capital
     Securities Guarantee Trustee's agents, nominees or custodians) and
     liabilities that might be incurred by it in complying with such request or
     direction, including such reasonable advances as may be requested by the
     Capital Securities Guarantee Trustee, PROVIDED, HOWEVER, that nothing
     contained in this Section 3.2(a)(vi) shall be taken to relieve the Capital
     Securities Guarantee Trustee, upon the occurrence of an Event of Default,
     of its obligation to exercise the rights and powers vested in it by this
     Series A Capital Securities Guarantee;

                                      -9-
<PAGE>   14

          (vii) \the Capital Securities Guarantee Trustee shall have no
     obligation to make any investigation into the facts or matters stated in
     any resolution, certificate, statement, instrument, opinion, report,
     notice, request, direction, consent, order, bond, debenture, note, other
     evidence of indebtedness or other paper or document, but the Capital
     Securities Guarantee Trustee, in its discretion, may make such further
     inquiry or investigation into such facts or matters as it may see fit;

          (viii) the Capital Securities Guarantee Trustee may execute any of the
     trusts or powers hereunder or perform any duties hereunder either directly
     or by or through agents, nominees, custodians or attorneys, and the Capital
     Securities Guarantee Trustee shall not be responsible for any misconduct or
     negligence on the part of any such person appointed with due care by it
     hereunder;

          (ix) any action taken by the Capital Securities Guarantee Trustee or
     its agents hereunder shall bind the Holders of the Series A Capital
     Securities, and the signature of the Capital Securities Guarantee Trustee
     or its agents alone shall be sufficient and effective to perform any such
     action; and no third party shall be required to inquire as to the authority
     of the Capital Securities Guarantee Trustee to so act or as to its
     compliance with any of the terms and provisions of this Series A Capital
     Securities Guarantee, both of which shall be conclusively evidenced by the
     Capital Securities Guarantee Trustee's or its agent's taking such action;

          (x) whenever in the administration of this Series A Capital Securities
     Guarantee the Capital Securities Guarantee Trustee shall deem it desirable
     to receive instructions with respect to enforcing any remedy or right or
     taking any other action hereunder, the Capital Securities Guarantee Trustee
     (i) may request instructions from the Holders of a Majority in Liquidation
     Amount of the Series A Capital Securities, (ii) may refrain from enforcing
     such remedy or right or taking such other action until such instructions
     are received, and (iii) shall be protected in conclusively relying on or
     acting in accordance with such instructions; and

          (xi) the Capital Securities Guarantee Trustee shall not be liable for
     any action taken, suffered, or omitted to be taken by it in good faith,
     without negligence, and reasonably believed by it to be authorized or
     within the discretion or rights or powers conferred upon it by this Series
     A Capital Securities Guarantee.

     (b)  No provision of this Series A Capital Securities Guarantee shall be
deemed to impose any duty or obligation on the Capital Securities Guarantee
Trustee to perform any act or acts or exercise any right, power, duty or
obligation conferred or imposed on it in any jurisdiction in which it shall be
illegal, or in which the Capital Securities Guarantee Trustee shall be
unqualified or incompetent in accordance with applicable law, to perform any
such act or acts or to exercise any such right, power, duty or obligation. No
permissive power or authority available to the Capital Securities Guarantee
Trustee shall be construed to be a duty.

     SECTION 3.3    NOT RESPONSIBLE FOR RECITALS OR ISSUANCE OF SERIES A
                    CAPITAL SECURITIES GUARANTEE

     The recitals contained in this Series A Capital Securities Guarantee shall
be taken as the statements of the Guarantor, and the Capital Securities
Guarantee Trustee does not assume any

                                      -10-
<PAGE>   15

responsibility for their correctness. The Capital Securities Guarantee Trustee
makes no representation as to the validity or sufficiency of this Series A
Capital Securities Guarantee.

                                   ARTICLE IV
                      CAPITAL SECURITIES GUARANTEE TRUSTEE

     SECTION 4.1    CAPITAL SECURITIES GUARANTEE TRUSTEE; ELIGIBILITY

     (a)  There shall at all times be a Capital Securities Guarantee Trustee
that shall

          (i) not be an Affiliate of the Guarantor; and

          (ii) be a corporation or other Person organized and doing business
     under the laws of the United States of America or any state or territory
     thereof or of the District of Columbia, or a corporation or other Person
     permitted by the Securities and Exchange Commission to act as an indenture
     trustee under the Trust Indenture Act, authorized under such laws to
     exercise corporate trust powers, having a combined capital and surplus of
     at least fifty million U.S. dollars ($50,000,000), and subject to
     supervision or examination by federal, state, territorial or District of
     Columbia authority; it being understood that if such corporation or other
     Person publishes reports of condition at least annually, pursuant to law or
     to the requirements of the supervising or examining authority referred to
     above, then, for the purposes of this Section 4.1(a)(ii) and to the extent
     permitted by the Trust Indenture Act, the combined capital and surplus of
     such corporation shall be deemed to be its combined capital and surplus as
     set forth in its most recent report of condition so published.

     (b)  If at any time the Capital Securities Guarantee Trustee shall cease
to be eligible to so act under Section 4.1(a), the Capital Securities Guarantee
Trustee shall immediately resign in the manner and with the effect set out in
Section 4.2(c).

     (c) If the Capital Securities Guarantee Trustee has or shall acquire any
"conflicting interest" within the meaning of Section 310(b) of the Trust
Indenture Act, the Capital Securities Guarantee Trustee and Guarantor shall in
all respects comply with the provisions of Section 310(b) of the Trust Indenture
Act.

     SECTION 4.2    APPOINTMENT, REMOVAL AND RESIGNATION OF CAPITAL SECURITIES
                    GUARANTEE TRUSTEE

     (a)  Subject to Section 4.2(b), the Capital Securities Guarantee Trustee
may be appointed or removed without cause at any time by the Guarantor except
during an Event of Default.

     (b)  The Capital Securities Guarantee Trustee shall not be removed in
accordance with Section 4.2(a) until a Successor Capital Securities Guarantee
Trustee has been appointed and has accepted such appointment by written
instrument executed by such Successor Capital Securities Guarantee Trustee and
delivered to the Guarantor.

     (c)  The Capital Securities Guarantee Trustee shall hold office until a
Successor Capital Securities Guarantee Trustee shall have been appointed or
until its removal or resignation. The

                                      -11-
<PAGE>   16

Capital Securities Guarantee Trustee may resign from office (without need for
prior or subsequent accounting) by an instrument in writing executed by the
Capital Securities Guarantee Trustee and delivered to the Guarantor, which
resignation shall not take effect until a Successor Capital Securities Guarantee
Trustee has been appointed and has accepted such appointment by instrument in
writing executed by such Successor Capital Securities Guarantee Trustee and
delivered to the Guarantor and the resigning Capital Securities Guarantee
Trustee.

     (d)  If no Successor Capital Securities Guarantee Trustee shall have been
appointed and accepted appointment as provided in this Section 4.2 within 60
days after delivery of an instrument of removal or resignation, the Capital
Securities Guarantee Trustee resigning or being removed may petition any court
of competent jurisdiction for appointment of a Successor Capital Securities
Guarantee Trustee. Such court may thereupon, after prescribing such notice, if
any, as it may deem proper, appoint a Successor Capital Securities Guarantee
Trustee.

     (e)  No Capital Securities Guarantee Trustee shall be liable for the acts
or omissions to act of any Successor Capital Securities Guarantee Trustee.

     (f)  Upon termination of this Series A Capital Securities Guarantee or
removal or resignation of the Capital Securities Guarantee Trustee pursuant to
this Section 4.2, the Guarantor shall pay to the Capital Securities Guarantee
Trustee all amounts due to the Capital Securities Guarantee Trustee accrued to
the date of such termination, removal or resignation.

                                   ARTICLE IV

                                   GUARANTEE

     SECTION 5.1     GUARANTEE

     The Guarantor irrevocably and unconditionally agrees to pay in full to the
Holders the Guarantee Payments (without duplication of amounts theretofore paid
by the Issuer), as and when due, regardless of any defense, right of set-off or
counterclaim that the Issuer may have or assert. The Guarantor's obligation to
make a Guarantee Payment may be satisfied by direct payment of the required
amounts by the Guarantor to the Holders or by causing the Issuer to pay such
amounts to the Holders.

     SECTION 5.2    WAIVER OF NOTICE AND DEMAND

     The Guarantor hereby waives notice of acceptance of this Series A Capital
Securities Guarantee and of any liability to which it applies or may apply,
presentment, demand for payment, any right to require a proceeding first against
the Issuer or any other Person before proceeding against the Guarantor, protest,
notice of nonpayment, notice of dishonor, notice of redemption and all other
notices and demands.

     SECTION 5.3    OBLIGATIONS NOT AFFECTED

     The obligations, covenants, agreements and duties of the Guarantor under
this Series A Capital Securities Guarantee shall in no way be affected or
impaired by reason of the happening from time to time of any of the following:

                                      -12-
<PAGE>   17

     (a)  the release or waiver, by operation of law or otherwise, of the
performance or observance by the Issuer of any express or implied agreement,
covenant, term or condition relating to the Series A Capital Securities to be
performed or observed by the Issuer;

     (b)  the extension of time for the payment by the Issuer of all or any
portion of the Distributions, Redemption Price, Liquidation Distribution or any
other sums payable under the terms of the Series A Capital Securities or the
extension of time for the performance of any other obligation under, arising out
of, or in connection with, the Series A Capital Securities;

     (c)  any failure, omission, delay or lack of diligence on the part of the
Holders to enforce, assert or exercise any right, privilege, power or remedy
conferred on the Holders pursuant to the terms of the Series A Capital
Securities, or any action on the part of the Issuer granting indulgence or
extension of any kind;

     (d)  the voluntary or involuntary liquidation, dissolution, sale of any
collateral, receivership, insolvency, bankruptcy, assignment for the benefit of
creditors, reorganization, arrangement, composition or readjustment of debt of,
or other similar proceedings affecting, the Issuer or any of the assets of the
Issuer;

     (e)  any invalidity of, or defect or deficiency in, the Series A Capital
Securities;

     (f)  the settlement or compromise of any obligation guaranteed hereby or
hereby incurred; (g)ab the consummation of the Exchange Offer (subject to
Section 7.1 hereof); or

     (h)  any other circumstance whatsoever that might otherwise constitute a
legal or equitable discharge or defense of a guarantor;

it being the intent of this Section 5.3 that the obligations of the Guarantor
with respect to the Guarantee Payments shall be absolute and unconditional under
any and all circumstances.

     There shall be no obligation of the Holders to give notice to, or obtain
consent of, the Guarantor with respect to the happening of any of the foregoing.

     SECTION 5.4    RIGHTS OF HOLDERS

     (a)  The Holders of a Majority in Liquidation Amount of the Series A
Capital Securities have the right to direct the time, method and place of
conducting any proceeding for any remedy available to the Capital Securities
Guarantee Trustee in respect of this Series A Capital Securities Guarantee or
exercising any trust or power conferred upon the Capital Securities Guarantee
Trustee under this Series A Capital Securities Guarantee.

     (b)  If the Capital Securities Guarantee Trustee fails to enforce this
Series A Capital Securities Guarantee, any Holder of the Series A Capital
Securities may institute a legal proceeding directly against the Guarantor to
enforce the Capital Securities Guarantee Trustee's rights under this Series A
Capital Securities Guarantee, without first instituting a legal proceeding
against the Issuer, the Capital Securities Guarantee Trustee or any other person
or entity. The Guarantor waives any right or remedy to require that any action
be brought first against the Issuer or any other person or entity before
proceeding directly against the Guarantor.

                                      -13-
<PAGE>   18

     SECTION 5.5    GUARANTEE OF PAYMENT

     This Series A Capital Securities Guarantee creates a guarantee of payment
and not of collection.

     SECTION 5.6    SUBROGATION

     The Guarantor shall be subrogated to all (if any) rights of the Holders of
Series A Capital Securities against the Issuer in respect of any amounts paid to
such Holders by the Guarantor under this Series A Capital Securities Guarantee;
PROVIDED, HOWEVER, that the Guarantor shall not (except to the extent required
by mandatory provisions of law) be entitled to enforce or exercise any right
that it may acquire by way of subrogation or any indemnity, reimbursement or
other agreement, in all cases as a result of payment under this Series A Capital
Securities Guarantee, if, at the time of any such payment, any amounts are due
and unpaid under this Series A Capital Securities Guarantee. If any amount shall
be paid to the Guarantor in violation of the preceding sentence, the Guarantor
agrees to hold such amount in trust for the Holders and to pay over such amount
to the Holders.

     SECTION 5.7    INDEPENDENT OBLIGATIONS

     The Guarantor acknowledges that its obligations hereunder are independent
of the obligations of the Issuer with respect to the Series A Capital
Securities, and that the Guarantor shall be liable as principal and as debtor
hereunder to make Guarantee Payments pursuant to the terms of this Series A
Capital Securities Guarantee notwithstanding the occurrence of any event
referred to in subsections (a) through (h), inclusive, of Section 5.3 hereof.

                                   ARTICLE IV

                   LIMITATION OF TRANSACTIONS; SUBORDINATION

     SECTION 6.1    LIMITATION OF TRANSACTIONS

     So long as any Capital Securities remain outstanding, the Guarantor shall
not (i) declare or pay any dividends or distributions on, or redeem, purchase,
acquire, or make a liquidation payment with respect to, any of the Guarantor's
capital stock, (ii) make any payment of principal of, or interest or premium, if
any, on or repay, repurchase or redeem any debt securities of the Guarantor
(including Other Debentures) that rank pari passu with or junior in right of
payment to the Debentures or (iii) make any guarantee payments with respect to
any guarantee by the Guarantor of the debt securities of any subsidiary of the
Guarantor (including Other Guarantees) if such guarantee ranks pari passu with
or junior in right of payment to the Debentures (other than (a) dividends or
distributions in shares of, or options, warrants, rights to subscribe for or
purchase shares of, common stock of the Guarantor, (b) any declaration of a
dividend in connection with the implementation of a shareholders' rights plan,
or the issuance of stock under any such plan in the future, or the redemption or
repurchase of any such rights pursuant thereto, (c) payments under this Series A
Capital Securities Guarantee and the Series B Capital Securities Guarantee, (d)
as a result of a reclassification of the Guarantor's capital stock or the
exchange or the conversion of one class or series of the Guarantor's capital
stock for another class or series of the Guarantor's capital stock, (e) the
purchase of fractional interests in shares of the Guarantor's capital stock
pursuant to the conversion or exchange provisions

                                      -14-
<PAGE>   19

of such capital stock or the security being converted or exchanged, and (f)
purchases of common stock related to the issuance of common stock or rights
under any of the Guarantor's benefit or compensation plans for its directors,
officers or employees or any of the Guarantor's dividend reinvestment plans) if
at such time (l) there shall have occurred any event of which the Guarantor has
actual knowledge that (A) is a Default or Event of Default (each as defined in
the Indenture) and (B) in respect of which the Guarantor shall not have taken
reasonable steps to cure, (2) if the Debentures are held by the Property
Trustee, the Guarantor shall be in default with respect to its payment of any
obligations under this Series A Capital Securities Guarantee or (3) the
Guarantor shall have given notice of its election of the exercise of its right
to commence an Extended Interest Payment Period as provided in the Indenture and
shall not have rescinded such notice, and such Extended Interest Payment Period,
or an extension thereof, shall have commenced and be continuing.

     SECTION 6.2    RANKING

     This Series A Capital Securities Guarantee will constitute an unsecured
obligation of the Guarantor and will rank (i) subordinate and junior in right of
payment to Senior Indebtedness (as defined in the Indenture), to the same extent
and in the same manner that the Debentures are subordinated to Senior
Indebtedness pursuant to the Indenture, it being understood that the terms of
Article XV of the Indenture shall apply to the obligations of the Guarantor
under this Series A Capital Securities Guarantee as if such Article XV were set
forth herein in full, (ii) pari passu with the most senior preferred or
preference stock now or hereafter issued by the Guarantor and with the Series B
Capital Securities Guarantee, any Other Guarantee and, except to the extent set
forth therein, the Common Securities Guarantee, any Other Common Securities
Guarantee, and any guarantee now or hereafter entered into by the Guarantor in
respect of any preferred or preference stock of any Affiliate of the Guarantor,
and (iii) senior to the Guarantor's common stock.

                                   ARTICLE VII

                                   TERMINATION

     SECTION 7.1    TERMINATION

     This Series A Capital Securities Guarantee shall terminate and be of no
further force and effect upon (i) full payment of the Redemption Price of all
Series A Capital Securities, (ii) the exchange of all Series A Capital
Securities for Series B Capital Securities pursuant to the Exchange Offer, (iii)
dissolution, winding up or liquidation of the Issuer, immediately following the
full payment of the amounts payable in accordance with the Declaration, or (iv)
the distribution of all of the Debentures to the Holders of the Trust
Securities. Notwithstanding the foregoing, this Series A Capital Securities
Guarantee will continue to be effective or will be reinstated, as the case may
be, if at any time any Holder of the Series A Capital Securities must restore
payment of any sums paid under the Series A Capital Securities or under this
Series A Capital Securities Guarantee.

                                      -15-
<PAGE>   20

                                  ARTICLE VIII

                                 INDEMNIFICATION

     SECTION 8.1    EXCULPATION

     (a)  No Indemnified Person shall be liable, responsible or accountable in
damages or otherwise to the Guarantor or any Covered Person for any loss, damage
or claim incurred by reason of any act or omission performed or omitted by such
Indemnified Person in good faith in accordance with this Series A Capital
Securities Guarantee and in a manner that such Indemnified Person reasonably
believed to be within the scope of the authority conferred on such Indemnified
Person by this Series A Capital Securities Guarantee or by law, except that an
Indemnified Person shall be liable for any such loss, damage or claim incurred
by reason of such Indemnified Person's negligence or willful misconduct with
respect to such acts or omissions.

     (b)  An Indemnified Person shall be fully protected in relying in good
faith upon the records of the Guarantor and upon such information, opinions,
reports or statements presented to the Guarantor by any Person as to matters the
Indemnified Person reasonably believes are within such other Person's
professional or expert competence and who has been selected with reasonable care
by or on behalf of the Guarantor, including information, opinions, reports or
statements as to the value and amount of the assets, liabilities, profits,
losses, or any other facts pertinent to the existence and amount of assets from
which Distributions to Holders of Series A Capital Securities might properly be
paid.

     SECTION 8.2    COMPENSATION AND INDEMNIFICATION

     The Guarantor agrees to pay to the Capital Securities Guarantee Trustee
such compensation for its services as shall be mutually agreed upon by the
Guarantor and the Capital Securities Guarantee Trustee. The Guarantor shall
reimburse the Capital Securities Guarantee Trustee upon request for all
reasonable out-of-pocket expenses incurred by it, including the reasonable
compensation and expenses of the Capital Securities Guarantee Trustee's agents
and counsel, except any expense as may be attributable to the negligence or bad
faith of the Capital Securities Guarantee Trustee.

     The Guarantor agrees to indemnify each Indemnified Person for, and to hold
each Indemnified Person harmless against, any and all loss, liability, damage,
action, suit, claim or expense incurred without negligence or bad faith on its
part, arising out of or in connection with the acceptance or administration of
the trust or trusts hereunder, including the costs and expenses (including
reasonable legal fees and expenses) of defending itself against, or
investigating, any claim or liability in connection with the exercise or
performance of any of its powers or duties hereunder. The provisions of this
Section 8.2 shall survive the termination of this Series A Capital Securities
Guarantee and shall survive the resignation or removal of the Capital Securities
Guarantee Trustee.

                                      -16-
<PAGE>   21

                                   ARTICLE IX

                                 MISCELLANEOUS

     SECTION 9.1    SUCCESSORS AND ASSIGNS

     All guarantees and agreements contained in this Series A Capital Securities
Guarantee shall bind the successors, assigns, receivers, trustees and
representatives of the Guarantor and shall inure to the benefit of the Holders
of the Series A Capital Securities then outstanding.

     SECTION 9.2    AMENDMENTS

     Except with respect to any changes that do not materially adversely affect
the rights of Holders of the Series A Capital Securities (in which case no
consent of such Holders will be required), this Series A Capital Securities
Guarantee may only be amended with the prior approval of the Holders of a
Majority in Liquidation Amount of the Series A Capital Securities. The
provisions of Section 12.2 of the Declaration with respect to meetings of
Holders of the Trust Securities apply to the giving of such approval. This
Series A Capital Securities Guarantee may not be amended, and no amendment
hereof that affects the Capital Securities Guarantee Trustee's rights, duties or
immunities hereunder or otherwise, shall be effective, unless such amendment is
executed by the Capital Securities Guarantee Trustee (which shall have no
obligation to execute any such amendment, but may do so in its sole discretion).

     SECTION 9.3    NOTICES

     All notices provided for in this Series A Capital Securities Guarantee
shall be in writing, duly signed by the party giving such notice, and shall be
delivered, telecopied or mailed by first class mail, as follows:

     (a)  If given to the Issuer, in care of the Administrative Trustee at the
Issuer's mailing address set forth below (or such other address as the Issuer
may give notice of to the Capital Securities Guarantee Trustee and the Holders
of the Series A Capital Securities):

                      BFOH CAPITAL TRUST I
                      c/o BancFirst Ohio Corp.
                      422 Main Street
                      Zanesville, Ohio 43701
                      Attention: Kim M. Taylor
                      Telephone: (740) 452-8444
                      Telecopier: (740) 455-5705

                                      -17-
<PAGE>   22

     (b)  If given to the Capital Securities Guarantee Trustee, at the Capital
Securities Guarantee Trustee's mailing address set forth below (or such other
address as the Capital Securities Guarantee Trustee may give notice of to the
Holders of the Series A Capital Securities):

                        WILMINGTON TRUST COMPANY
                        Rodney Square North
                        1100 North Market Street
                        Wilmington, Delaware 19890-0001
                        Attention: Corporate Trust Administration
                        Telephone: (302) 651-1000
                        Telecopier: (302) 651-8882

     (c)  If given to the Guarantor, at the Guarantor's mailing address set
forth below (or such other address as the Guarantor may give notice of to the
Capital Securities Guarantee Trustee and the Holders of the Series A Capital
Securities):

                        BANCFIRST OHIO CORP.
                        422 Main Street
                        Zanesville, Ohio 43701
                        Attention: Kim M. Taylor
                        Telephone: (740) 452-8444
                        Telecopier: (740) 455-5705

     (d)  If given to any Holder of the Series A Capital Securities, at the
address set forth on the books and records of the Issuer.

     All such notices shall be deemed to have been given when received in
person, telecopied with receipt confirmed, or mailed by first class mail,
postage prepaid except that if a notice or other document is refused delivery or
cannot be delivered because of a changed address of which no notice was given,
such notice or other document shall be deemed to have been delivered on the date
of such refusal or inability to deliver.

     SECTION 9.4    EXCHANGE OFFER

     In the event an Exchange Offer Registration Statement (as defined in the
Registration Rights Agreement) becomes effective and the Issuer exchanges any
Series B Capital Securities for Series A Capital Securities in the Exchange
Offer, the Guarantor will enter into the Series B Capital Securities Guarantee,
which will be in substantially the same form as this Series A Capital Securities
Guarantee, with respect to the Series B Capital Securities. Each Holder, by its
acceptance hereof, agrees to be bound by the Registration Rights Agreement.

     SECTION 9.5    BENEFIT

     This Series A Capital Securities Guarantee is solely for the benefit of the
Holders of the Series A Capital Securities and, subject to Section 3.1(a), is
not separately transferable from the Series A Capital Securities.

                                      -18-
<PAGE>   23

     SECTION 9.6    GOVERNING LAW

     THIS SERIES A CAPITAL SECURITIES GUARANTEE SHALL BE GOVERNED BY, AND
CONSTRUED AND INTERPRETED IN ACCORDANCE WITH, THE LAWS OF THE STATE OF NEW YORK
WITHOUT REGARD TO CONFLICT OF LAW PRINCIPLES THEREOF.

     This Series A Capital Securities Guarantee is executed as of the day and
year first above written.

                                     BANCFIRST OHIO CORP.,
                                     as Guarantor

                                     By:
                                        --------------------------------------
                                        Gary N. Fields
                                        President and Chief Executive Officer

                                     WILMINGTON TRUST COMPANY,
                                     as Capital Securities Guarantee Trustee

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

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