[BALLARD SPAHR ANDREWS & INGERSOLL, LLP LETTERHEAD APPEARS HERE]




                                                                      EXHIBIT 12


                               September 10, 2001


AIM Advisor Funds                           AIM Funds Group
11 Greenway Plaza                           11 Greenway Plaza
Suite 100                                   Suite 100
Houston, TX 77046-1173                      Houston, TX 77046-1173

                  RE:      FEDERAL INCOME TAX CONSEQUENCES OF THE
                           REORGANIZATION OF AIM ADVISOR FLEX FUND

Ladies and Gentlemen:

                  You have requested our opinion regarding certain United States
federal income tax consequences in connection with the transfer of the property,
assets, and goodwill of AIM Advisor Flex Fund ("Flex Fund"), an investment
portfolio of AIM Advisor Funds ("AIM Advisor"), a Delaware business trust, to
AIM Balanced Fund ("Balanced Fund"), an investment portfolio of AIM Funds Group
("AIM Funds Group"), a Delaware business trust, in exchange solely for shares of
beneficial interest of Balanced Fund ("Balanced Fund Shares") issued by AIM
Funds Group directly to Flex Fund Shareholders, and Balanced Fund's assumption
of Flex Fund's liabilities, and the termination of Flex Fund as a designated
series of shares of AIM Advisor, all pursuant to the Agreement and Plan of
Reorganization dated as of June 13, 2001 between AIM Advisor, AIM Funds Group
and A I M Advisors, Inc., a Delaware corporation (the "Agreement") (the
transaction in its entirety being hereinafter referred to as the
"Reorganization"). Capitalized terms used in this letter without definition
shall have the meanings given them in the Agreement.

                  For purposes of this opinion, we have examined and relied upon
the accuracy and completeness of the facts, information, covenants, statements
and representations contained in originals or copies of the Agreement, the
exhibits attached thereto, the Registration Statement on Form N-14 filed by AIM
Funds Group on May 11, 2001 with the Securities and Exchange Commission, and
such other documents and instruments as we have deemed necessary or appropriate.
In our examination of the foregoing materials, we have assumed the genuineness
of all signatures, legal capacity of natural persons, the authenticity of all
documents submitted to us as originals and the conformity to the original
documents of all documents submitted to us as copies. We have assumed that such
documents reflect all the material facts relating to the Reorganization. In
addition, we have assumed that the Reorganization will be consummated in



AIM Advisor Funds
AIM Funds Group
September 10, 2001
Page 2

accordance with the terms of such documents and that none of the material terms
and conditions contained therein will have been waived or modified prior to the
consummation of the Reorganization.

                  In rendering this opinion, we are relying upon the
representations and warranties made by AIM Advisor and AIM Funds Group in the
Agreement as well as on letters of representation of even date that we have
received from the officers of AIM Advisor and AIM Funds Group, copies of which
are attached as Exhibits A and B hereto. We have not been asked to, nor have we
undertaken to, verify the accuracy of these and other representations made to
us. In this regard, we have assumed that any representation made to the best of
knowledge, "to the knowledge" or similarly qualified is correct without such
qualification. As to all matters in which a person making a representation has
represented that such person either is not a party to, does not have, or is not
aware of, any plan or intention, understanding or agreement, we have likewise
assumed that there is in fact no such plan, intention, understanding, or
agreement.

                  Based upon and subject to the foregoing, it is our opinion
that, for federal income tax purposes:

                  1. The transfer of the assets of Flex Fund to Balanced Fund in
exchange for Balanced Fund Shares distributed directly to Flex Fund
Shareholders, as provided in the Agreement, will constitute a "reorganization"
within the meaning of Section 368(a) of the Code and each of Flex Fund and
Balanced Fund will be "a party to a reorganization" within the meaning of
Section 368(b) of the Code.

                  2. In accordance with Section 361(a) and Section 361(c)(1) of
the Code, no gain or loss will be recognized by Flex Fund on the transfer of its
assets to Balanced Fund solely in exchange for Balanced Fund Class A Shares,
Balanced Fund Class B Shares and Balanced Fund Class C Shares or on the
distribution of Balanced Fund Class A Shares, Balanced Fund Class B Shares and
Balanced Fund Class C Shares to Flex Fund Shareholders.

                  3. In accordance with Section 1032 of the Code, no gain or
loss will be recognized by Balanced Fund upon the receipt of assets of Flex Fund
in exchange for Balanced Fund Class A Shares, Balanced Fund Class B Shares and
Balanced Fund Class C Shares issued directly to Flex Fund Shareholders.

                  4. In accordance with Section 354(a)(1) of the Code, no gain
or loss will be recognized by Flex Fund Shareholders on the receipt of Balanced
Fund Class A Shares, Balanced Fund Class B Shares and Balanced Fund Class C
Shares in exchange for Flex Fund Shares.

                  5. In accordance with Section 362(b) of the Code, the basis to
Balanced Fund of the assets of Flex Fund will be the same as the basis of such
assets in the hands of Flex Fund immediately prior to the Reorganization.




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AIM Funds Group
September 10, 2001
Page 3


                  6. In accordance with Section 358(a) of the Code, a Flex Fund
Shareholder's basis for Balanced Fund Class A Shares, Balanced Fund Class B
Shares or Balanced Fund Class C Shares received by the Flex Fund Shareholder
will be the same as his basis for Flex Fund Shares exchanged therefor.

                  7. In accordance with Section 1223(1) of the Code, a Flex Fund
Shareholder's holding period for Balanced Fund Class A Shares, Balanced Fund
Class B Shares or Balanced Fund Class C Shares will be determined by including
Flex Fund Shareholder's holding period for Flex Fund Shares exchanged therefor,
provided that the Flex Fund Shareholder held such Flex Fund Shares as a capital
asset.

                  8. In accordance with Section 1223(2) of the Code, the holding
period with respect to the assets of Flex Fund transferred to Balanced Fund in
the Reorganization will include the holding period for such assets in the hands
of Flex Fund.

                  We express no opinion as to the tax consequences of the
Reorganization except as expressly set forth above, or as to any transaction
except the Reorganization. We also note that certain Flex Fund Shareholders may
be subject to special rules because of their particular federal income tax
status and that the tax consequences of the Reorganization to such Flex Fund
Shareholders may accordingly differ from the ones of general application that
are described above. This opinion is intended to satisfy the mutual condition
precedent to the Reorganization set forth in Section 6.2(f) of the Agreement, is
being furnished to you solely for that purpose, and may not be relied upon by
any other person without our express written consent.

                  Our opinion is based upon the Code, Treasury regulations
(proposed, temporary and final) promulgated thereunder, judicial decisions,
interpretative rulings of the Internal Revenue Service and such other
authorities as we have considered relevant, all as in effect on the date hereof.
All such legal authorities are subject to change, either prospectively or
retroactively. We are not undertaking hereby any obligation to advise you of any
changes in the applicable law subsequent to the date hereof, even if such
changes materially affect the tax consequences of the Reorganization that are
set forth above.

                  If any of the facts, assumptions or representations on which
our opinion is based is incorrect, we expect you to advise us so that we may
consider the effect, if any, on our opinion.



AIM Advisor Funds
AIM Funds Group
September 10, 2001
Page 4


                  Our opinion has no binding effect on the Internal Revenue
Service or the courts of any jurisdiction. No assurance can accordingly be given
that, if the matter were contested, a court would agree with the legal
conclusions set forth above.

                                    Sincerely,
                                    /s/ BALLARD, SPAHR, ANDREWS & INGERSOLL, LLP