Production from the Bakken shale play in North Dakota was a standout in terms of gains for Marathon Oil, which posted a $386 million loss in the second quarter.

For all of North America, the company said in its second quarter report net production averaged 274,000 barrels of oil equivalent per day. That represents a 21 percent increase year-on-year, but 3 percent lower than first quarter 2015.

Marathon President and Chief Executive Officer Lee Tillman said the net decline was in part because of less spending on exploration and production.

"Capital spending in the quarter was down about 40 percent sequentially as we've moderated activity levels in the U.S. resource plays," he said in a statement.

In North Dakota, the company said it averaged 61,000 boe per day from the Bakken shale basin, a 22 percent increase from second quarter 2014 and a 7 percent gain from the previous quarter. Marathon attributed the gain to improved efficiency in its shale drilling operations.

State data from North Dakota show 75 rigs actively exploring for or producing oil or natural gas in the state, relatively unchanged in recent weeks. Thursday's rig count, however, is 60 percent below this date in 2014.

The North Dakota Industrial Commission reported oil production in May, the last full month for which government data are published, at 1.2 million barrels per day, just shy of the all-time record posted in December 2014.

Sami Yahya, an energy analyst from Bentek, the forecasting unit of reporting agency Platts, said early this week companies in the Bakken shale are learning to do more with less in an era of depressed crude oil prices.

Elsewhere in U.S. shale, Marathon posted mixed results. In the Eagle Ford shale play in Texas, the company's net production was 32 percent higher than second quarter than 2014, but 8 percent less than first quarter 2015. In Oklahoma, production was up 33 percent year-on-year and relatively unchanged from the previous quarter.

Tillman said his company was focused on things it can control, like well productivity and operational efficiencies, instead of things it can't, like crude oil prices.

"Looking to the second half of the year, we expect to maintain production levels and achieve our year-over-year production growth of 5-7 percent for the total company and 20 percent in the U.S. resource plays," he said.