Opinion Letter – Outside Counsel – S-4 Registered Securities – Exxon Mobil Corp.

Exxon Mobil Corporation

5959 Las Colinas Boulevard

Irving, Texas 75039-2298

Ladies and Gentlemen:

We have acted as counsel to Exxon Mobil Corporation, a New Jersey corporation
(“Parent“), in connection with (i) the Merger, as defined and
described in the Agreement and Plan of Merger dated as of December 13, 2009 (the
“Merger Agreement“) among Parent, ExxonMobil Investment
Corporation, a Delaware corporation and a wholly-owned subsidiary of Parent
(“Merger Subsidiary“) and XTO Energy Inc., a Delaware
corporation (“Company“) and (ii) the preparation and filing of
the related Registration Statement on Form S-4 (the “Registration
Statement“), which includes the Proxy Statement/Prospectus (the
“Proxy Statement/Prospectus“), filed with the Securities and
Exchange Commission (the “Commission“). Unless otherwise
indicated, each capitalized term used herein has the meaning ascribed to it in
the Merger Agreement.

In connection with this opinion, we have examined the Merger Agreement, the
Registration Statement, the Proxy Statement/Prospectus, the representation
letters of Parent (together with Merger Subsidiary) and the Company delivered to
us for purposes of this opinion (the “Representation Letters“)
and such other documents as we have deemed necessary or appropriate in order to
enable us to render our opinion. In such examination, we have assumed the
genuineness of all signatures, the legal capacity of natural persons, the
authenticity of all documents submitted to us as originals, the conformity to
original documents of all documents submitted to us as duplicates or certified
or conformed copies, and the authenticity of the originals of such latter
documents. We have not, however, undertaken any independent investigation of any
factual matter set forth in any of the foregoing. For purposes of this opinion,
we have assumed, with your permission, (i) that the Merger will be consummated
in the manner described in Merger Agreement and the Proxy Statement/Prospectus,
(ii) the statements concerning the Merger set forth in the Merger Agreement and
the Proxy Statement/Prospectus are true, complete and correct and will remain
true, complete and correct at all times up to and including the Effective Time,
(iii) that the representations made by Parent (together with Merger Subsidiary)
and the Company pursuant to Section 8.06(b) of the Merger

Agreement are and will be accurate and complete, and (iv) any representations
made in the Merger Agreement or the Representation Letters “to the knowledge
of”, or based on the belief of Parent, Merger Subsidiary or the Company or
similarly qualified are true, complete and correct and will remain true,
complete and correct at all times up to and including the Effective Time, in
each case without such qualification. We have also assumed that the parties have
complied with and, if applicable, will continue to comply with, the obligations,
covenants, and agreements contained in the Merger Agreement. In addition, our
opinion is based solely on the documents that we have examined, the additional
information that we have obtained, and the representations made and to be made
by Parent and the Company referred to above, which we have assumed will be true
as of the Effective Time.

Based upon the foregoing, and subject to the assumptions and qualifications
set forth herein, we hereby confirm our opinion set forth in the discussion in
the Proxy Statement/Prospectus under the heading “Material U.S. Federal Income
Tax Consequences of the Merger.”

We express our opinion herein only as to those matters specifically set forth
above and no opinion should be inferred as to the tax consequences of the Merger
under any state, local or foreign law, or with respect to other areas of U.S.
federal taxation. We are members of the Bar of the State of New York, and we do
not express any opinion herein concerning any law other than the federal law of
the United States.

This opinion is furnished to you solely for use in connection with the
Registration Statement. We hereby consent to the filing of this opinion as an
exhibit to the Registration Statement and to the references to our firm name in
the Proxy Statement/Prospectus in connection with the references to this opinion
and the material U.S. federal income tax consequences of the Merger. In giving
such consent, we do not thereby admit that we are in the category of persons
whose consent is required under Section 7 of the Securities Act of 1933, as
amended, or the rules and regulations of the Commission thereunder.