Duke Energy's fourth quarter earnings fell 33 percent as mild weather reduced demand for electricity.

Duke earned $288 million, or 22 cents per share, down from $427 million, or 32 cents per share, in the fourth quarter of 2010.

The year-earlier results were helped by a sale of a fiber optic company. This year, Duke incurred costs associated with its proposed merger with in-state rival Progress Energy.

Duke's earnings, adjusted to remove the effects of special items, rose 14 percent to 24 cents per share. Revenue was $3.37 billion. Analysts polled by FactSet expected earnings of 21 cents per share on revenue of $3.36 billion.

Results were helped by strong performance of its international operations.

For the full year, Duke Energy Corp. earned $1.71 billion on revenue of $14.53 billion.

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