Occidental Petroleum bid $76 a share for Anadarko Petroleum on Wednesday, higher than a previous offer by Chevron for the oil and gas driller.

The new Occidental offer, which was sent via a letter to Anadarko's board on Wednesday, is half cash and half stock, specifically $38 in cash and 0.6094 Occidental shares. It values Anadarko at $57 billion, including debt.

Chevron announced an agreement on April 12 to buy Anadarko for $33 billion in cash and stock, valuing the company at $65 a share. CNBC later reported there was another bidder for Anadarko from Occidental, which was offering mid-$70s per share before Chevron stepped in with its offer.

After Occidental disclosed its bid, Anadarko shares surged 11.6%, rising above $71.

The Chevron offer is a 75% stock and 25% cash transaction. The breakup fee for the Chevron-Anadarko deal is said to be 3% of the deal, sources said.

"Anadarko has great assets," Occidental CEO Vicki Hollub said in a interview on CNBC's "Squawk Box" on Wednesday. "We are the right acquirer ... because we can get the most out of the shale."

Hollub said she considers this a friendly offer, even though Anadarko may not see it that way. The offer is 20% above where Anadarko was trading on Tuesday.

Anadarko confirmed that it had received the Occidental's unsolicited bid. The company said its board will carefully review the proposal to determine the best course of action for shareholders.

"The Anadarko board has not made any determination as to whether Occidental's proposal constitutes, or could reasonably be expected to result in, a superior proposal under the terms of the Chevron Merger Agreement," the Company said in a statement.

Occidental shares fell about half a percent on Wednesday. Chevron's stock was down 3.1%.

"We are confident the transaction agreed to by Chevron and Anadarko will be completed," said Kent Robertson, manager for global external affairs for Chevron.

— With reporting by Tom DiChristopher