U.S. power producers, led by American Electric Power Co , Dominion Resources and Constellation Energy Group , posted quarterly earnings that topped Wall Street expectations even as demand from industrial customers weakened because of the recession.

The effects of the weak economy are obvious, said Michael Morris, Ohio-based AEP's chairman, president and chief executive.

Electricity sold to industrial customers decreased from the same period last year. Off-system sales -- electricity sold into the wholesale market -- were down significantly.

Baltimore-based Constellation reported higher-than-expected second-quarter results and increased its earnings forecast for the full year 2009, but said demand destruction from the recession and mild weather had been higher than expected.

We expect power prices to remain weak in the near term and rebound in 2011 and 2012 as the economy recovers from the current recession, Chief Executive Mayo Shattuck said on a conference call.

Dominion, of Richmond, Virginia, reported stronger-than-expected second-quarter earnings, but trimmed its forecast for next year because of uncertainty about an economic rebound.

While it is certainly possible for us to earn within the original range, we think based on the uncertainties of the current environment, it is prudent to make this change, the company said.

Albuquerque-based smaller utility PNM Resources
, which posted a second-quarter profit on an ongoing basis, also said the slowdown impacted demand, though to a lesser degree, and backed its 2009 earnings view.

While we can't say the recession is over, during the second quarter the current recession has had less of an impact on our business than it had before, Chief Operating Officer Pat Vincent-Collawn said on a conference call with analysts.

Newark-based Public Service Enterprise Group (PSEG)
reported second-quarter operating profit in-line with analysts estimates, but said abnormally cool weather conditions through the end of July would challenge its ability to meet the upper end of its full-year profit view.

A contraction in economic activity, coupled with the impact of abnormally cool weather conditions during the month of June, resulted in a 15 percent reduction in generation for the quarter, the company said.

AEP shares were up 1 percent at $31.03, while Constellation shares were down 2 percent at $28.52 Friday morning on the New York Stock Exchange. Dominion and PNM shares were almost flat $34.52 and $12.17, respectively. PSEG shares were down 1 percent at $32.89.

(Reporting by Matt Daily and Steve James in New York, Adveith Nair and Arup Roychoudhury in Bangalore; Editing by Steve Orlofsky, Jarshad Kakkrakandy)