The takeover is expected to be a stock-based deal at a modest premium to Progress’ current market value of $13.1bn.
The companies could announce a deal as soon as today before Wall Street opens, although talks were believed to be ongoing yesterday.
A spokesperson for Duke Energy said the firm did not comment on speculation yesterday, while Progress could not be reached for comment.
Both electricity-generating companies are based in North Carolina and serve clients in North and South Carolina. Duke serves some markets in the American Midwest and Progress also supplies customers in Florida.
If Duke does acquire Progress, the enlarged company would have revenues of more than $22bn based on 2009 results.
Duke last year lost out on a bid for the US assets of German utility E.ON but its chief executive, Jim Rogers, an industry veteran who has led various utilities in the past 21 years, has widely been seen as hungry to make acquisitions.