Exhibit 5.1

                                October 3, 2000

Carreker Corporation
4055 Valley View Lane, Suite 1000
Dallas, Texas 75244

    Re:  Registration Statement on Form S-3

Dear Sirs:

    We have acted as counsel for Carreker Corporation, a Delaware corporation
(the "Company"), and certain stockholders of the Company in connection with
the registration under the Securities Act of 1933, as amended (the "Act"), of
an aggregate of 4,600,000 shares of the Company's Common Stock, $.01 par
value per share (the "Securities"). We have examined such documents and
questions of law as we have deemed necessary to render the opinion expressed
below.

    Based upon the foregoing, we are of the opinion that the Securities, when
issued and sold as described in the above-referenced Registration Statement,
will be legally issued, fully paid and nonassessable.

    We consent to the filing of this opinion as an exhibit to the
Registration Statement and to the reference to our firm in the prospectus
under the caption "Legal Matters." In giving this consent, we do not thereby
admit that we come within the category of persons whose consent is required
under Section 7 of the Act or the rules and regulations of the Securities and
Exchange Commission promulgated thereunder.

                                       Sincerely,

                                       LOCKE LIDDELL & SAPP LLP

                                       By: /s/ JOHN B. MCKNIGHT
                                          ---------------------
                                          John B. McKnight