U.S. power producers American Electric Power Co , Dominion Resources and Constellation Energy Group posted quarterly earnings on Friday 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, 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.

Ohio-based AEP, one of the largest U.S. utilities, posted a 12 percent increase in second-quarter profit. Earnings rose to $316 million, or 67 cents per share, from $281 million, or 70 cents per share, in the year-ago quarter.

Excluding one-time items, AEP earned 68 cents per share, to top the 62 cents per share that analysts had on average expected, according to Reuters Estimates.

Revenue slipped 8.6 percent to $3.2 billion.

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.

Its net income rose to $454 million, or 76 cents per share, from $298 million, or 51 cents per share, in the year-ago quarter. Adjusted operating earnings rose to 68 cents per share, topping the 64 cents per share expected by analysts, according to Reuters Estimates.

Revenue climbed 1.5 percent to $3.45 billion.

Dominion lowered it forecast for operating earnings in 2010 to a range of $3.20 to $3.40 per share, from $3.33 to $3.50 per share.

Baltimore-based Constellation too posted higher-than-expected second-quarter results and increased its earnings forecast for the full year 2009.

Net income applicable to common stockholders was $8.1 million, or 4 cents a share, compared with $171.5 million, or 95 cents a share, in the year-ago quarter, Constellation said.

Adjusted earnings for the quarter were $1.08 a share, compared with $1.82 in the same quarter last year.

Total revenue fell about 19 percent to $3.86 billion.

Analysts, on average, expected earnings of 76 cents a share, before special items, on revenue of $3.57 billion, according to Reuters Estimates. For full-year 2009, the company now expects earnings of $3.10 to $3.30 per share, up from $2.90 to $3.20 a share.

(Reporting by Matt Daily and Steve James; Editing by Steve Orlofsky)