[LETTERHEAD OF BRACEWELL & PATTERSON, L.L.P.]


                                                                     Exhibit 5.1


                               December 20, 2000



Prosperity Bancshares, Inc.
3040 Post Oak Boulevard
Houston, Texas 77056

Ladies and Gentlemen:

We have acted as counsel to Prosperity Bancshares, Inc., a Texas corporation
(the "Company"), in connection with the proposed merger of Commercial
Bancshares, Inc. ("Commercial") with and into the Company pursuant to the terms
of an Agreement and Plan of Reorganization dated as of November 8, 2000, by and
among the Company and Commercial (the "Merger Agreement"). Pursuant to the
Merger Agreement, the Company will issue shares of its Common Stock, par value
$1.00 per share (the "Common Stock"), to the shareholders of Commercial.  The
Company has filed a Registration Statement on Form S-4 (the "Registration
Statement") under the Securities Act of 1933, as amended (the "Securities Act"),
with the Securities and Exchange Commission with respect to the Common Stock to
be issued pursuant to the Merger Agreement.

In our capacity as counsel to the Company in connection with the Merger
Agreement, we have examined the originals, or copies certified to our
satisfaction, of such records, agreements, instruments and documents as we have
deemed necessary as a basis for the opinion hereinafter expressed.  In all such
examinations we have assumed the genuineness of all signatures, the authenticity
of all documents, certificates and records submitted to us as originals, the
conformity to original documents, certificates and records of all documents,
certificates and records submitted to us as copies, and the truthfulness of all
statements of fact contained therein.  We also have assumed, with respect to all
parties to agreements or instruments relevant hereto other than the Company with
respect to the Merger Agreement, that such parties had the requisite power and
authority (corporate or other) to execute, deliver and perform such agreements
or instruments, that such agreements or instruments have been duly authorized by
all requisite action (corporate or otherwise), executed and delivered by such
parties and that such agreements and instruments are the valid, binding and
enforceable obligations of such parties.  As to various matters of fact relevant
to the opinion hereinafter expressed, we have relied upon, and have assumed the
accuracy of, certificates and oral or written statements and other information
of or from public officials, officers and representatives of the Company and
others.


Prosperity Bancshares, Inc.
December 20,
Page 2

Based on the foregoing, and subject to the limitations set forth herein, and
having due regard for such legal considerations as we deem relevant, we are of
the opinion that, when the shares of the Company's Common Stock are issued upon
consummation of the merger pursuant to the terms of the Merger Agreement, such
shares will be validly issued, fully paid and non-assessable.  The foregoing
opinion is based on and is limited to the corporate laws of the State of Texas
and the relevant laws of the United States of America, and we render no opinion
with respect to the laws of any other jurisdiction.

We hereby consent to the filing of this opinion with the Securities and Exchange
Commission as an exhibit to the Registration Statement and to the use of our
name therein under the caption "Legal Matters."  In giving this consent, we do
not admit that we are in the category of persons whose consent is required under
Section 7 of the Securities Act.

                              Very truly yours,

                              /s/ Bracewell & Patterson, L.L.P.

                              Bracewell & Patterson, L.L.P.