A unit of Denver’s Armstrong Oil & Gas Inc. and Spanish energy giant Repsol SA have announced what they call “the largest U.S. onshore conventional hydrocarbons discovery in 30 years” on the north slope of Alaska, near an earlier find by the two companies.

In a statement Thursday, Repsol said it and Anchorage, Alaska-based Armstrong Energy made the discovery over the winter at a pair of wells dubbed “Horseshoe.”

They said the find “could amount to approximately 1.2 billion barrels of recoverable light oil.” But production may not begin for another four years.

Armstrong owns 75 percent of the Horseshoe wells and Repsol the other 25 percent, and Armstrong is developing the site.

Repsol said it has been exploring in Alaska since 2008, and has been drilling with partner Armstrong since 2011.

Read more at the Denver Business Journal: http://bit.ly/2mbDSmb