Exhibit 8.1

SIDLEY AUSTIN LLP

787 SEVENTH AVENUE

NEW YORK, NY 10019

(212) 839 5300

(212) 839 5599 FAX

BEIJING

BRUSSELS

CHICAGO

DALLAS

FRANKFURT

GENEVA

HONG KONG

HOUSTON

LONDON

LOS ANGELES

NEW YORK

PALO ALTO

SAN FRANCISCO

SHANGHAI

SINGAPORE

SYDNEY

TOKYO

WASHINGTON, D.C.

FOUNDED 1866

April 23, 2012

BNP Paribas Quantitative Strategies, LLC,

as Managing Owner of

STREAM Exchange Traded Trust

c/o BNP Paribas Quantitative Strategies, LLC

787 Seventh Avenue

New York, New York 10019

Re:

STREAM Exchange Traded Trust

Pre-Effective Amendment No. 4 to the

Registration Statement on Form S-1

Dear Sir or Madam:

We have acted as your counsel in connection with the preparation and filing with the Securities and Exchange Commission (the “SEC”) under the Securities Act of 1933, as amended (the “Act”), of Pre-Effective Amendment No. 4 to the Registration Statement on Form S-1, filed with the SEC on or about April 23, 2012 (the “Registration Statement”) of STREAM Exchange Traded Trust (the “Trust”), a Delaware statutory trust organized on April 30, 2010 and converted into a series trust on May 13, 2011 and with respect to STREAM S&P Dynamic Roll Global Commodities Fund, one of the Trust’s series (the “Fund”).

We have reviewed such documents, questions of law and fact and other matters as we have deemed pertinent for the purpose of this opinion. Based upon the foregoing, we hereby confirm our opinion contained under the heading “Material U.S. Federal Income Tax Considerations” in the prospectus constituting a part of the Registration Statement (the “Prospectus”) that the Fund will be classified as a partnership for U.S. federal income tax purposes.

We also advise you that the tax discussion under the captions “The Risks You Face,” paragraphs (50), (51) and (52), “Summary – U.S. Federal Income Tax Considerations,” and “Material U.S. Federal Income Tax Considerations” in the Prospectus correctly describes the material aspects of the U.S. federal income tax treatment to a United States individual taxpayer, as of the date hereof, of an investment in the Fund.

Sidley Austin (NY) LLP is a Delaware limited liability partnership doing business as Sidley Austin LLP and practicing in affiliation with other Sidley Austin partnerships.

LOGO

BNP Paribas Quantitative Strategies, LLC

April 23, 2012

Page 2

Our opinion represents our best legal judgment with respect to the proper U.S. federal income tax treatment of the Fund and United States individual taxpayers investing in the Fund, based on the materials reviewed. Our opinion assumes the accuracy of the facts as represented in documents reviewed or as described to us and could be affected if any of the facts as so represented or described are inaccurate.

We hereby consent to the filing of this opinion as an Exhibit to the Registration Statement and all references to our firm included in or made a part of the Registration Statement. 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 Act or the rules and regulations of the SEC thereunder.

Very truly yours,

/s/ Sidley Austin LLP

STREAM Exchange Traded Trust S-1/A