Oil production in North Dakota increased 1 percent despite obvious signs of a slowdown in the state's shale reserve areas, state data show.

The North Dakota Industrial Commission said oil production in March, the last full month for which data are available, was 1.19 million barrels per day, up from the 1.18 million bpd from February but down from the 1.22 million bpd in December, the all-time high.

The increase comes despite a drop in the number of rigs exploring for or producing oil and natural gas in the No. 2 oil producer in the nation.

"The drilling rig count dropped 25 from February to March, 17 more from March to April, and has since fallen 8 more from April to today," the NDIC said in its monthly report.

The rig count of 83 is the lowest since January 2010.

Oil companies are spending less on exploration and production because crude oil markets have been depressed for nearly a year. That leaves energy companies with less capital to invest in exploration and production.

The NDIC said the price of oil "is by far the biggest driver" of the slump in rig numbers in the state, followed by tax measures, goals set for the amount of gas captured during oil production and reserve conditioning rules.

Rig counts have served as a barometer for the health of an oil industry coping with lower crude oil prices. The data presents a mixed picture, however, as some companies are reporting that improved drilling efficiency means they're able do more with fewer deployments.

More than 90 percent of the state's oil production comes from Bakken shale. Nearly all of the drilling now targets the state's shale formations.