The hedge fund Elliott Management is hoping to block Warren E. Buffett’s $9 billion takeover bid for Energy Future Holdings, the bankrupt Texas power giant, by working on an even higher offer.

Elliott, the biggest creditor to Energy Future, on Monday published correspondence with the utility operator that included descriptions of an alternative takeover bid that it was working on, which carried a price of about $9.3 billion.

All told, the hedge fund wrote in a July 5 letter to Energy Future, such a plan — if it came together — would value the company and its prized Oncor utility at $18.5 billion, including assumed debt. The takeover bid from Mr. Buffett’s Berkshire Hathaway, which Energy Future accepted on Friday, carried a total enterprise value of roughly $18 billion.

A spokesman for Elliott declined to comment beyond the public materials. Oncor did not immediately respond to a request for comment.