It probably had to happen someday. The oil boom in North Dakota has made it the nation's No. 2 oil producing state, edging past Alaska in March.

This comes just four months after North Dakota surpassed California in oil output -- a dramatic testament to drilling techniques that are extracting ever more crude from previously inaccessible shale layers.

The state of North Dakota released data Monday showing that in March 6,603 wells in the state produced 17.8 million barrels of oil, or 575,490 barrels per day. That's just ahead of Alaska's 17.6 million barrels, according to that state's monthly production data.

To be fair, said Bruce Hicks, assistant director of North Dakota's Oil and Gas Division, Alaska's oil production has slipped recently, and its output can fluctuate month to month, so the two states probably will stay close for a time.

"It's not a race," he added. "There is no doubt that we're on the increase and they're on the decrease. It was inevitable that we would at some point reach what their production is."

Texas, whose output was 49 million barrels or 1.7 million barrels per day in February, still reigns as No. 1 and likely will stay in that spot because it's also witnessing a shale-oil boom.

North Dakota has rapidly increased output in the Bakken shale and Three Forks formations in the western part of the state. Horizontal drilling methods adapted to oil exploration have produced a fivefold increase in production in just five years.

The ultimate output of North Dakota's oil patch has been variously estimated at 800,000 barrels per day to more than 1 million barrels per day. With more than 200 drilling rigs working in the region, the output is steadily rising.

"Some people feel we are halfway up the curve and some think maybe two-thirds of the way," said Ron Ness, president of the North Dakota Petroleum Council. "We have been on a rapid incline. Just over the past year, it has increased 46 percent."

Over the next 15 years, there could be 20,000 to 30,000 oil wells in North Dakota, Hicks said.

Ness said North Dakota and Alaska each supply about 9 percent of the nation's oil needs. Natural gas also is produced in North Dakota, although about a third of it is being flared because of limited pipeline capability.

At Northern Oil and Gas, based in Wayzata, vice president for business development Erik Nerhus said company officials were excited to see North Dakota reach the No. 2 spot.

"As a significant producer of crude oil originating from North Dakota, we have witnessed first-hand the pace of drilling in the Bakken and Three Forks plays continuing to accelerate and our own acreage position turn into production at an increasing rate," Nerhus said in an e-mail.

He said production will grow as drillers switch to pad drilling, in which multiple wells are drilled from one location. Northern Oil, which is about the 10th-largest leaseholder in the Bakken and Three Forks plays, expects to produce approximately 4 million barrels of crude oil equivalents this year, he added.

David Shaffer • 612-673-7090