Chevron said its net U.S. production so far during second quarter 2014 was higher than first quarter in part because of increases from the Permian shale basin.

Chevron posted an interim update on second quarter operations through May. Total oil equivalent produced from its U.S. portfolio through May was 665 million barrels per day, compared to 640 million boe per day for the full first quarter.

"U.S. net oil-equivalent production was higher compared to the first quarter, primarily due to less maintenance activity in the Gulf of Mexico and increased production in the Permian Basin," the company said Thursday.

Net Permian production increased 58 percent from 2007 to reach 1.35 million bpd last year, which represents 18 percent of total U.S. crude oil production.

Internationally, Chevron said its output was down marginally.

The company warned in an interim first quarter report its net production had declined and said investors should be prepared for lower-than-expected profits.

"Earnings for the second quarter 2014 are expected to be higher than first quarter 2014 as a result of gains on asset sales and an absence of impairments in the prior quarter," it said Thursday.