The Alaska-based subsidiary of Denver’s Armstrong Oil & Gas Inc. and Repsol SA are calling their recent discovery “the largest U.S. onshore conventional hydrocarbons discovery in 30 years.” On the north slope of Alaska, Anchorage and Repsol claim they found what could amount to around 1.2 billion barrels of recoverable light oil, according to the Denver Business Journal.

The companies made the discovery this past winter near an earlier find, at a pair of wells called Horseshoe. Armstrong owns 75 percent of the wells and Repsol owns the remainder. Armstrong is developing the site; however, production may not begin for another four years.

The recent find is an expansion of a perviously known oil formation called the Pikka Unit, discovered in 2015 by Repsol and Armstrong. Again Armstrong owns the majority at 51 percent and Repsol the remainder.

Learn more: Denver Business Journal > Denver Energy Company, partner claim biggest U.S. onshore oil find in 30 years