Halliburton is negotiating to buy Baker Hughes in a deal that would combine two of the world's largest oil field services companies, US media reported Thursday.
The reports in The Wall Street Journal and New York Times did not give any price for the deal.
But Baker Hughes' market capitalization was about $22 billion before the reports while Halliburton's valuation was more than $45 billion.
The reports came just before the markets closed and sent Baker Hughes shares soaring 15.2 percent to $58.75, for a $25 billion valuation.
Halliburton meanwhile finished the day up 1.1 percent at $43.79.
A combined Halliburton-Baker Hughes would become a potent rival to the industry power Schlumberger, whose shares fell 2.6 percent following the news.