A boom in shale oil production that’s forecast to raise North Dakota’s output to 2 million barrels a day has boosted the number of rigs drilling for crude in the Williston Basin to the highest level in almost two years.

Rigs targeting oil in the Williston Basin, home to the Bakken and Three Forks shale formations, jumped by four to 198, the most since October 2012, data posted on Baker Hughes Inc.’s website show. The play accounted for almost half of this week’s growth in U.S. oil rigs, which rose to a record 1,601, the Houston-based field services company said. Rigs drilling for gas in the U.S. slid by nine to 329.

The total energy rig count has almost doubled from five years ago as producers use horizontal drilling and hydraulic fracturing to reach oil and gas deposits in U.S. shale formations. The boom will increase domestic crude production in 2015 to the highest level in 45 years, shrinking imports to the U.S., federal government forecasts show.

“The Williston is doing better than I had anticipated,” James Williams, president of energy consulting WTRG Economics in London, Ark., said by telephone today. “This may be due to increased drilling in the Three Forks formation, and at least a part of it can be explained by prices.”

The discount for Bakken at Clearbrook, Minn., versus the U.S. benchmark West Texas Intermediate crude has narrowed 36% in the past year, data compiled by Bloomberg show. Earlier this month, the oil strengthened to its highest level versus WTI since June.

The rig count in North Dakota will rise above 200 next year, Lynn Helms, director of the state’s Department of Mineral Resources, said in a presentation yesterday. The state’s oil output is expected to peak between 2015 and 2025 at 2 million barrels a day, the agency said.

Whiting Petroleum Corp. agreed in July to buy Kodiak Oil & Gas Corp. for about $3.8 billion in stock, turning it into the dominant crude producer in the Bakken.

Oil production jumped 248,000 barrels a day in the week ended Sept. 12 to 8.84 million, the highest level since 1986, Energy Information Administration data show. Oil supplies climbed 3.67 million barrels to 362.3 million.

West Texas Intermediate crude for October delivery fell 66 cents, or 0.7%, to settle at $92.41 a barrel on the New York Mercantile Exchange, down 13% in the past year.

U.S. gas stockpiles rose 90 billion cubic feet last week to 2.891 trillion, according to the EIA. Supplies were 13% below the five-year average and 12% below year-earlier levels.

Natural gas for October delivery sank 7.3 cents, or 1.9% , to $3.837 per million British thermal units today on the Nymex, up 3.2 percent in the past year.