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This announcement is neither an offer to purchase nor a solicitation of an offer
to sell Shares (as defined below). The Offer (as defined below) is made solely
by the Offer to Purchase dated August 9, 2001 (the "Offer to Purchase"), and the
related Letter of Transmittal and any amendments or supplements thereto and is
not being made to (nor will tenders be accepted from or on behalf of) holders of
Shares in any jurisdiction in which the making of the Offer or the acceptance
thereof would not be in compliance with the laws of such jurisdiction. In any
jurisdiction in which the securities, blue sky or other laws require the Offer
to be made by a licensed broker or dealer, the Offer shall be deemed made on
behalf of the Purchaser (as defined below) by Sandler O'Neill & Partners, L.P.,
the Dealer Manager (as defined below), or by one or more registered brokers or
dealers that are licensed under the laws of such jurisdiction.

                      NOTICE OF OFFER TO PURCHASE FOR CASH
                    ALL OUTSTANDING SHARES OF COMMON STOCK
                                       OF
                   NATIONAL BANCSHARES CORPORATION OF TEXAS
                                       AT
                             $24.75 NET PER SHARE
         (SUBJECT TO ADJUSTMENT AS PROVIDED IN THE OFFER TO PURCHASE)
                                       BY
                             NBC ACQUISITION CORP.,
                          A WHOLLY-OWNED SUBSIDIARY OF
                      INTERNATIONAL BANCSHARES CORPORATION

NBC Acquisition Corp., a Texas corporation (the "Purchaser") and a wholly-owned
subsidiary of International Bancshares Corporation, a Texas corporation
("Parent"), is offering to purchase all outstanding shares of common stock, par
value $.001 per share (the "Shares"), of National Bancshares Corporation of
Texas, a Texas corporation (the "Company"), at a price of $24.75 per Share,
subject to adjustment as provided in the Offer to Purchase, net to the seller in
cash, without interest thereon, upon the terms and subject to the conditions set
forth in the Offer to Purchase and in the related Letter of Transmittal (which,
together with any amendments or supplements thereto, collectively constitute the
"Offer"). Tendering shareholders who have Shares registered in their names and
who tender directly to The Bank of New York (the "Depositary") will not be
obligated to pay brokerage fees or commissions or, except as set forth in the
Letter of Transmittal, transfer taxes on the purchase of Shares by the Purchaser
pursuant to the Offer. Shareholders who hold their Shares through a broker or
bank should consult with such institution as to whether it charges any service
fees. The purpose of the Offer is to acquire for cash as many outstanding Shares
as possible as a first step in acquiring the entire equity interest in the
Company. Following the consummation of the Offer, the Purchaser intends to
effect the Merger (as defined below).

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THE OFFER AND WITHDRAWAL RIGHTS WILL EXPIRE AT 12:00 MIDNIGHT, NEW YORK CITY
TIME, ON FRIDAY, SEPTEMBER 7, 2001, UNLESS THE OFFER IS EXTENDED.
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The Offer is conditioned upon, among other things, there being validly tendered
and not withdrawn prior to the Expiration Date (as defined below) that number of
Shares that represent at least two-thirds of all of the Shares (determined on a
fully diluted basis) on the date of purchase.

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The Offer is being made pursuant to an Agreement and Plan of Merger dated as of
July 30, 2001 (the "Merger Agreement"), among Parent, the Purchaser and the
Company pursuant to which, following the consummation of the Offer and the
satisfaction or waiver of certain conditions, the Purchaser will be merged with
and into the Company, with the Company surviving the merger as a wholly owned
subsidiary of Parent (the "Merger"). At the effective time of the Merger, each
outstanding Share (other than Shares owned by Parent, the Purchaser or the
Company or any subsidiary of Parent or the Company or by shareholders, if any,
who are entitled to and properly exercise dissenters' rights under Texas law),
will be converted into the right to receive the price per Share paid pursuant to
the Offer in cash, without interest, as set forth in the Merger Agreement and
described in the Offer to Purchase.

Concurrently with the execution and delivery of the Merger Agreement, Parent
entered into agreements with certain officers and directors of the Company
owning in the aggregate 508,867 Shares (exclusive of stock options) pursuant to
which such officers and directors have agreed to validly tender (and not to
withdraw) in the Offer all of such Shares, which Shares represent approximately
13.5% of the outstanding Shares (or approximately 12.3% of the outstanding
Shares on a fully diluted basis).

THE BOARD OF DIRECTORS OF THE COMPANY HAS APPROVED AND ADOPTED THE MERGER
AGREEMENT AND THE TRANSACTIONS CONTEMPLATED THEREBY AND DETERMINED THAT THE
OFFER AND THE MERGER ARE ADVISABLE AND FAIR TO AND IN THE BEST INTERESTS OF THE
COMPANY AND ITS SHAREHOLDERS. ACCORDINGLY, THE BOARD OF DIRECTORS OF THE COMPANY
RECOMMENDS THAT SHAREHOLDERS TENDER THEIR SHARES IN THE OFFER.

For purposes of the Offer, the Purchaser will be deemed to have accepted for
payment pursuant to the Offer, and thereby purchased, Shares properly tendered
and not properly withdrawn as, if and when the Purchaser gives oral or written
notice to the Depositary of the Purchaser's acceptance for payment of such
Shares pursuant to the Offer. Upon the terms and subject to the conditions of
the Offer, payment for Shares accepted for payment pursuant to the Offer will be
made by deposit of the purchase price therefor with the Depositary, which will
act as agent for tendering shareholders for the purpose of receiving payment
from the Purchaser and transmitting payment to tendering shareholders. In all
cases, payment for Shares accepted for payment pursuant to the Offer will be
made only after timely receipt by the Depositary of (a) the certificates for
such Shares or timely confirmation of book-entry transfer of such Shares into
the Depositary's account at the Book-Entry Transfer Facility (as defined in the
Offer to Purchase) pursuant to the procedures set forth in Section 2 of the
Offer to Purchase, (b) a Letter of Transmittal (or a facsimile thereof),
properly completed and duly executed, with any required signature guarantees or,
in the case of a book-entry transfer, an Agent's Message (as defined in the
Offer to Purchase) and (c) any other documents required by the Letter of
Transmittal. UNDER NO CIRCUMSTANCES WILL INTEREST BE PAID ON THE PURCHASE PRICE
OF THE SHARES TO BE PAID BY THE PURCHASER, REGARDLESS OF ANY EXTENSION OF THE
OFFER OR ANY DELAY IN PAYING FOR SUCH SHARES.

The term "Expiration Date" means 12:00 midnight, New York City time, on Friday,
September 7, 2001, unless and until the Purchaser, in its sole discretion (but
subject to the terms of the Merger Agreement), shall have extended the period of
time during which the Offer is open, in which event the term "Expiration Date"
shall mean the latest time and date at which the Offer, as so extended by the
Purchaser, will expire. The Purchaser may, without the consent of the Company,
and expressly reserves the right to, extend the Offer, and thereby delay
acceptance for payment of, and the payment for, any Shares, by giving oral or
written notice of such extension to the Depositary, (a) if at the Expiration
Date of the Offer any of the conditions to the Purchaser's obligation to
purchase Shares are not satisfied, until such time as such conditions are
satisfied or waived, (b) for any period required by any rule, regulation,
interpretation or position of the Securities Exchange Commission (the
"Commission") or the staff thereof applicable to the Offer or (c) for any reason
on one or more occasions for a period of not more than five business days beyond
the latest expiration date that would otherwise be permitted under clause (a) or
(b) of this sentence. If all of the conditions to the Offer are not satisfied on
the Expiration Date, then,

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provided that all such conditions are reasonably capable of being satisfied, the
Purchaser will extend the Offer from time to time until such conditions are
satisfied or waived; provided that the Purchaser shall not be required to extend
the Offer beyond December 31, 2001. Any such extension will be followed by a
public announcement thereof no later than 9:00 a.m., New York City time, on the
next business day after the previously scheduled Expiration Date. During any
such extension, all Shares previously tendered and not withdrawn will remain
subject to the Offer, subject to the right of a tendering shareholder to
withdraw such shareholder's Shares.

Except as otherwise provided below, tenders of Shares made pursuant to the Offer
are irrevocable. Shares tendered pursuant to the Offer may be withdrawn pursuant
to the procedures set forth below at any time prior to the Expiration Date and,
unless theretofore accepted for payment pursuant to the Offer, may also be
withdrawn at any time after October 8, 2001. For a withdrawal to be effective, a
written or facsimile transmission notice of withdrawal must be timely received
by the Depositary at one of its addresses set forth on the back cover of the
Offer to Purchase and must specify the name of the person having tendered the
Shares to be withdrawn, the number of Shares to be withdrawn and the name of the
registered holder of the Shares to be withdrawn, if different from the name of
the person who tendered the Shares. If certificates for Shares have been
delivered or otherwise identified to the Depositary, then prior to the physical
release of such certificates, the serial numbers shown on such certificates must
be submitted to the Depositary and, unless such Shares have been tendered by an
Eligible Institution (as defined in the Offer to Purchase), any and all
signatures on the notice of withdrawal must be guaranteed by an Eligible
Institution. If Shares have been delivered pursuant to the procedure for
book-entry transfer as set forth in Section 2 of the Offer to Purchase, any
notice of withdrawal must also specify the name and number of the account at the
Book-Entry Transfer Facility to be credited with the withdrawn Shares and
otherwise comply with the Book-Entry Transfer Facility's procedures. Withdrawals
of tenders of Shares may not be rescinded, and any Shares properly withdrawn
will thereafter be deemed not validly tendered for purposes of the Offer.
However, withdrawn shares may be retendered by again following one of the
procedures described in Section 2 of the Offer to Purchase at any time prior to
the Expiration Date. Under the Merger Agreement and pursuant to Rule 14d-11 of
the General Rules and Regulations under the Securities Exchange Act of 1934, as
amended (the "Exchange Act"), the Purchaser may, subject to certain conditions,
elect to provide a subsequent offering period following the Expiration Date. The
Purchaser does not currently intend to provide a subsequent offering period in
the Offer, although it reserves the right to do so in its sole discretion. Under
the Exchange Act, no withdrawal rights apply to Shares tendered during a
subsequent offering period and no withdrawal rights apply during the subsequent
offering period with respect to Shares tendered in the Offer and accepted for
payment. See Section 1 of the Offer to Purchase. All questions as to the form
and validity (including time of receipt) of notices of withdrawal will be
determined by the Purchaser, in its sole discretion, which determination will be
final and binding. None of the Purchaser, Parent, the Company, the Depositary,
the Information Agent, the Dealer Manager or any other person will be under any
duty to give notification of any defects or irregularities in any notice of
withdrawal or incur any liability for failure to give any such notification.

The Company has provided the Purchaser with the Company's shareholder lists and
security position listings for the purpose of disseminating the Offer to holders
of Shares. The Offer to Purchase and the related Letter of Transmittal and other
relevant materials will be mailed to record holders of Shares and furnished to
brokers, dealers, banks, trust companies and similar persons whose names, or the
names of whose nominees, appear on the Company's shareholder lists, or, if
applicable, who are listed as participants in a clearing agency's security
position listing, for subsequent transmittal to beneficial owners of Shares.

The Purchaser expressly reserves the right to waive any condition to the Offer
or modify the terms of the Offer, subject to (a) the terms of the Merger
Agreement, which contains certain conditions that may not

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be waived and modifications that may not be made without the consent of the
Company, and (b) the rules and regulations of the Commission.

The information required to be disclosed by paragraph (d)(1) of Rule 14d-6 of
the General Rules and Regulations under the Exchange Act is contained in the
Offer to Purchase and is incorporated herein by reference.

THE OFFER TO PURCHASE AND LETTER OF TRANSMITTAL CONTAIN IMPORTANT INFORMATION
AND SHOULD BE READ CAREFULLY AND IN THEIR ENTIRETY BEFORE ANY DECISION IS MADE
WITH RESPECT TO THE OFFER.

Questions and requests for assistance may be directed to the Information Agent
or the Dealer Manager, as set forth below. Requests for copies of the Offer to
Purchase, the Letter of Transmittal and all other tender offer materials may be
directed to the Information Agent as set forth below, or brokers, dealers,
banks, trust companies or other nominees, and copies will be furnished promptly
at the Purchaser's expense. No fees or commissions will be payable to brokers,
dealers or other persons (other than the Dealer Manager, the Depositary and the
Information Agent) for soliciting tenders of Shares pursuant to the Offer.

                   The Information Agent for the Offer is:

                               [INNISFREE LOGO]

                         501 Madison Avenue, 20th Floor
                           New York, New York 10022
                Banks and Brokers Call Collect: (212) 750-5833
                  All Others Call Toll-Free: (888) 750-5834

                      The Dealer Manager for the Offer is:

                        SANDLER O'NEILL & PARTNERS, L.P.
                       Two World Trade Center, 104th Floor
                             New York, New York 10048
                           (866) 732-1234 (toll free)

August 9, 2001

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