Marathon Oil Corporation — by far the biggest oil and gas producer in Park County — is exiting the area and the state of Wyoming.

The company announced this week that it sold its Wyoming wells and other operations in the state to another large and locally established producer, Merit Energy Company.

The $870 million sale to Merit is expected to close by the middle of this year.

It will end Marathon’s more than 100-year-long run in Wyoming; the company had celebrated its first century in the state in 2012.

“Sad day,” Park County Commissioner Loren Grosskopf said of the sale.

Exiting Wyoming is part of the publicly traded company’s efforts to remain viable amid low oil prices.

Between the end of 2014 and the end of 2015, Marathon shed roughly 660 positions and 20 percent of its payroll across the multi-national company, the Casper Star-Tribune reported. Local jobs were among those cut.

Marathon has been increasingly focusing on its three most profitable areas of operation: the Eagle Ford Shale in South Texas, the Bakken Shale in North Dakota and eastern Montana and the Oklahoma Resource Basins.

Rumblings of a possible sale of Marathon’s Wyoming business first surfaced in the Star-Tribune in late November and the company confirmed it was shopping its assets last month.

To date, Marathon has sold off approximately $1.3 billion worth of assets in what the company calls its “non-core asset divestiture program.”

“Ongoing portfolio management continues to drive the simplification and concentration of our portfolio to lower risk, higher return U.S. resource plays and support our 2016 objective of balance sheet protection,” Marathon Oil president and CEO Lee Tillman said in a Monday statement.

Marathon’s stock rose on the news of the sale. In a note to investors reported on by CNBC, Deutsche Bank called the sale price “favorable” and “a major positive takeaway” for the company.

Barron’s quoted a Citigroup analyst, Robert Morris, as saying Marathon’s Wyoming operations accounted for about 4 percent of its current production.

Marathon mostly operated in the Wind and Big Horn basins. Its largest local presence is in the Oregon Basin field south of Cody, but the company has wells across the area, including in the Garland Field near Byron.

The company produced nearly 5.77 million barrels of oil and more than 4.72 million mcf (thousand cubic feet) of natural gas to lead all producers in the Big Horn Basin last year, according to Wyoming Oil and Gas Conservation Commission statistics.

Merit came in third for oil production in the Big Horn Basin, with more than 1.35 barrels, while producing no natural gas.

Marathon has also been — far and away — Park County’s largest taxpayer. It singlehandedly accounted for roughly 30 percent of the property taxes collected in the county last year, said Park County Assessor Pat Meyer.

The next-biggest taxpayer was Encore Energy, which accounted for about 8.5 percent of the county’s assessed valuation. Merit came in as third-largest, accounting for more than 3 percent of Park County’s assessed value.

Historically, Merit has had its largest local presence in Hot Springs County, with extensive operations in the Hamilton Dome area northwest of Thermopolis.

The privately held company says on its website that it owns an interest in over 10,000 wells across 10 states, including neighboring Utah, Colorado and Nebraska.

Park County officials are anxious to see what happens following the sale of Marathon’s assets.

“We’ll have to wait and see what Merit’s going to do, but you know there’s going to be duplication of services,” commissioner Grosskopf said, adding, “We don’t know what the financial impact is, but (we’ll) be cautiously optimistic that Merit sees more opportunity here, because Marathon hasn’t been doing big-end development for a long time.”

According to Morris’ analysis posted on Barron’s website, Marathon last drilled a well in Wyoming in 2013.

Both Grosskopf and Commissioner Joe Tilden said regulations from the federal Bureau of Land Management have made for a tough environment for drilling in the Big Horn Basin.

“It may not be economically feasible to come back,” Tilden said, adding, “It’s pretty bleak out there.”

Meyer, the assessor, was more optimistic.

“It’ll start coming back. This time it will be with Merit,” he predicted. “They’re not going to leave that oil in the ground. It’s too much money.”

Marathon’s Cody office is housed in the Park County Complex, a building it used to own, but sold to the county in 2005.

Marathon officials negotiated a new, five-year lease of their rental space last summer and persuaded commissioners to give them a small discount.

The contract says that if Marathon terminates its lease within the first three years of the deal, it must pay the county a $100,000 penalty.

At an early August meeting, Marathon attorney Kirby Iler of Cody had told commissioners not to read too much into the clause.

“There’s no plans to exit Cody,” Iler had said.