The board of US midsized oil company Anadarko said Occidental’s new offer last week “could reasonably be expected to result in a ‘Superior Proposal’,” Anadarko said in statement. “The Anadarko board's determination allows Anadarko to resume negotiations with Occidental in accordance with the Chevron Merger Agreement.”

US oil companies Chevron and Occidental have been in a tug-of-war for Anadarko, whose assets are centered on the shale-rich Permian Basin in Texas.

Occidental's April 24 proposal “reflects significant improvement with respect to indicative value, terms and conditions, and closing certainty as compared to any previous proposal Occidental made to Anadarko,” according to the statement.

The proposed takeover valued Anadarko at $76 a share, compared to the $65 offered by Chevron, and expressed disappointment that Anadarko had ignored earlier bids that Occidental said were superior.

Chevron Chief Executive Mike Wirth expressed confidence its deal - which was approved by Anadarko's board - would be completed, but indicated the company could walk away if the price becomes unreasonable.

Some analysts expect Chevron to raise its bid for Anadarko following the Occidental push.

Shares of Anadarko slipped 0.6 percent to $72.40 in pre-market trading.

Occidental shed 2.2 percent to $59.95, while Chevron gained 1.2 percent to $118.48.