Warren Buffett's Berkshire Hathaway (BRK.A) (BRK.B) said Wednesday that it will "stand firm" on its $9 billion offer to buy 80% of Oncor Electric Delivery Co LLC, refusing to up its bid in the face of competition from Paul Singer's hedge fund Elliott Management, Reuters reported.

Elliott is Berkshire's biggest competition in the acquisition, besting Berkshire's bid with a $9.3 billion offer. Berkshire's deal values Oncor at $18.1 billion, but Elliott's puts it at $18.5 billion.

Elliott owns a major position in Oncor parent-company Energy Future's biggest block of debt. The firm purchased a new slice of debt in an impaired class of notes Wednesday to ensure it can block Buffett's deal.

Elliott has until August 21 to formalize its offer. If it doesn't submit U.S. bankruptcy court its completed offer by then, the court is set to approve Berkshire's offer for Oncor. If Berkshire's deal falls through, it could be hit with a $270 million termination fee.

Berkshire stock traded down 0.21% to $178.19 Thursday morning.

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