North Dakota’s oil business continues to show signs of recovery this spring, though sluggish oil prices are casting a cloud on the industry.

North Dakota, the nation’s second largest oil producing state, produced 1.05 million barrels of petroleum per day in April, up 2.4 percent from March, according to data released Tuesday from the North Dakota Department of Mineral Resources.

The number of drill rigs operating in the state now stands at 55, up from 50 in May. A rising rig count is an indicator of more oil field activity, as operators drill new wells. The rig count hit an all-time high of 218 in May 2012 and fell below 30 for three months last spring. The rig count has been climbing this year.

“Fifty-five rigs looks like a confident industry,” Lynn Helms, director of the state mineral resources department, said in a monthly conference call with reporters.

Still, Helms noted in a written monthly report that things could be better. “Low oil price[s] associated with very high crude oil inventories continued to limit the drilling rig count.”

Oil prices had hovered above $50 a barrel for much of the time from December through mid-April. But they have been more volatile since, even after major oil producing nations last month said they would continue to curtail output amid a global supply glut. West Texas Intermediate (WTI), the benchmark U.S. crude oil, is priced around $46 per barrel.

Generally, North Dakota’s oil investment prospects fall when oil drops below $50 a barrel for a sustained period of time.

“If WTI drops below $45/barrel for more than 30 days, rig count is expected to drop,” wrote Helms, adding he expects WTI prices to average around $50 per barrel for the year.

North Dakota, and all U.S. shale oil producing regions, have seen conditions improve since late last year. Oil field companies have been hiring back workers in recent months, after laying off thousands during the oil bust in 2015 and 2016.

Helms noted that contractors in North Dakota are having trouble finding enough workers to man fracking crews, which blast water and sand through wells. North Dakota labor markets are already tight. And the state is competing for workers with Southwest shale oil fields, which are considerably more active now than those in North Dakota.

Also in April, North Dakota’s natural gas production hit a record high as more gas collecting infrastructure has come online.