But the largest U.S. natural gas distribution utility, an unyielding hedge fund, and a Delaware bankruptcy judge now present one of the biggest challenges to the billionaire's legendary discipline.

The rival bid for Oncor was disclosed on Friday by Energy Future's biggest creditor, billionaire Paul Singer's hedge fund Elliott Management Corp.

Berkshire said on Friday that its bid had won support from key stakeholders, including the staff of the Public Utility Commission of Texas, the regulator that has to approve the sale of Oncor.

Even if regulatory concerns trump price considerations, and Berkshire's bid for Oncor prevails on Sunday over that of Sempra, a San Diego-based utility, the sale has to be approved on Monday by U.S. Bankruptcy Judge Christopher Sontchi in Wilmington, Delaware.

Complicating Buffett's hunt for bargains are soaring stock market valuations and competition from private equity firms with a lot of funds to spend, as well as from companies with anemic earnings growth that are turning to acquisitions for a recovery in their fortunes.