Elk Basin is the Bighorn Basin’s border-straddling giant: a bold anticline lying across the Wyoming–Montana line in Park County, Wyoming and Carbon County, Montana. Midwest Refining opened it on October 8, 1915 with a well flowing up to 150 barrels a day of high-grade light oil from the Frontier — but the field’s real scale emerged a generation later, when the Tensleep came in during 1942 and the Madison in 1946. Deep pays, unitization, and fluid injection ultimately pushed cumulative recovery past half a billion barrels.
Geologist George Ketchum is credited with recognizing the Elk Basin anticline as a likely oil trap, and Midwest Refining’s wildcat proved him right on October 8, 1915, flowing up to 150 barrels a day of light, high-grade crude from shallow Frontier sands. A camp grew in the remote, scenic basin as First World War demand pulled development along, and the field settled into steady but modest production — about eight million barrels through the beginning of 1927.
The transformation came from depth. In 1942 drillers reached the Pennsylvanian Tensleep sandstone, which proved so prolific that 129 wells were ultimately completed in it; in 1946 the Madison limestone discovery well flowed roughly 200 barrels a day and opened yet another major pay. The numbers tell the story starkly: although Elk Basin had produced since 1915, some 99.8 percent of its cumulative recovery came after 1942, driven by the deep zones, accelerated drilling, unitization, and fluid injection.
Mid-century unitization organized the field for pressure maintenance and waterflooding across its stacked reservoirs — Tensleep, Madison, Frontier, and deeper Paleozoic zones — under major-company operatorship, and Elk Basin became one of the Rocky Mountain region’s premier engineered floods. Production has long since matured, with the old units passing to later operators, but the field’s century-plus of output places cumulative recovery on the order of 550 million barrels across the two states.
Elk Basin is a large, sharply defined anticline on the northeastern rim of the Bighorn Basin, its axis crossing the Wyoming–Montana state line. The shallow Cretaceous Frontier sands hosted the 1915 discovery, but the giants below define the field: the Pennsylvanian Tensleep sandstone and the Mississippian Madison limestone, with additional deep pays in the Bighorn and Jefferson. Strong structure, thick Paleozoic reservoirs, and good continuity made the field ideal for unit-wide pressure maintenance — the engineering that produced nearly all of its half-billion-barrel recovery.
Elk Basin’s recovery story is unitization plus water. Once the Tensleep and Madison came in during the 1940s, operators unitized the field and implemented fluid-injection projects — pressure maintenance and waterflooding — that swept the thick Paleozoic reservoirs far more completely than primary depletion could have. The result ranks among the Rockies’ most effective conventional floods: a field that produced eight million barrels in its first twelve years went on to deliver hundreds of millions after 1942. Long-settled flood operations still underpin the field’s remaining production today.
Elk Basin interests come with a two-state wrinkle: the field straddles the Wyoming–Montana line, so leases, pooling, and probate practice can differ on either side of a single structure, and inherited interests often need curative work in both states. The production itself is classic late-life flood output — modest, steady, and long-lived. We buy minerals and royalties in Park County, Wyoming and Carbon County, Montana directly, handle the cross-border title work at our expense, and provide free written offers.
County-level well data, production charts, and selling guides for the counties this field spans:
Because the big reservoirs lay deeper than early drilling reached. The Tensleep sandstone came in during 1942 and the Madison limestone in 1946, and with unitization and fluid injection those zones delivered some 99.8 percent of the field’s cumulative recovery.
It adds steps, not obstacles. Wyoming and Montana handle conveyances, probate, and recording separately, so an interest spanning both may need documents filed in each state. We routinely manage that curative work at our expense as part of a purchase.
Yes. The field is deep into its mature phase, but the unitized Tensleep and Madison flood operations that powered its mid-century surge still support steady production more than a century after the 1915 discovery well.