Exhibit 15
November 4, 2011
Avista Corporation
Spokane, Washington
We have reviewed, in accordance with the standards of the Public Company Accounting Oversight Board (United States), the unaudited interim financial information of Avista Corporation and subsidiaries for the periods ended September 30, 2011 and 2010, as indicated in our report dated November 4, 2011; because we did not perform an audit, we expressed no opinion on that information.
We are aware that our report referred to above, which is included in your Quarterly Report on Form 10-Q for the quarter ended September 30, 2011, is incorporated by reference in Registration Statement Nos. 2-81697, 2-94816, 033-54791, 333-03601, 333-22373, 333-58197, 333-33790, 333-47290, and 333-126577 on Form S-8; and in Registration Statement Nos. 333-155657 and 333-163609 on Form S-3.
We are also aware that the aforementioned report, pursuant to Rule 436(c) under the Securities Act of 1933, is not considered a part of the Registration Statement prepared or certified by an accountant or a report prepared or certified by an accountant within the meaning of Sections 7 and 11 of that Act.
/s/ Deloitte & Touche LLP
Seattle, Washington
November 4, 2011