EXHIBIT 5.1
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                       [MCCARTHY TETRAULT LLP LETTERHEAD]



                                                            April 3, 2007


Securities and Exchange Commission
450 Fifth Street NW
Washington, DC 20549

Dear Sirs:

         Re:   REGISTRATION STATEMENT ON FORM S-8 OF METHANEX CORPORATION

         We have  acted  as  Canadian  counsel  to  Methanex  Corporation  (the
"Company") in connection with the filing of the  above-referenced  registration
statement (the "Registration Statement") relating to the registration of common
shares of the Company  (the  "Shares")  issuable  upon the  exercise of options
granted or to be granted under the Methanex  Corporation Stock Option Plan 2006
(the "Plan"). In connection therewith, we have considered such questions of law
and have examined and relied upon such  resolutions,  records,  certificates of
public  officials  and  officers  of the  Company  and other  documents  deemed
necessary or appropriate to enable us to render the opinion expressed below.

         Based on the foregoing,  it is our opinion that the Shares will,  upon
the exercise of such options in accordance  with the terms of the Plan, and the
receipt by the  Company of the  exercise  price  under  such  options  for such
Shares,  be validly  issued and  outstanding  as fully paid and  non-assessable
shares.

         We hereby  consent to the filing of this  opinion as an exhibit to the
Registration  Statement and to all references to our firm included in or made a
part of the Registration Statement.

                                               Yours Truly,


                                               /s/ McCARTHY TETRAULT LLP