The acquisition would double Exxon Mobil’s resources in the Permian Basin to 6 billion barrels of oil equivalent, as well as an “exceptional Delaware Basin position in a proven multi-stacked play that can generate attractive returns in a low-price environment,” said Darren Woods, Exxon Mobil CEO, in a prepared statement.

The Irving, Texas oil company said it plans to issue $5.6 billion in shares to purchase the companies owned by the Bass family in Fort Worth, and it could start making additional incremental cash payments of $1 billion in 2020, through 2032

These firms, including the private producer BOPCO, have estimated resources of 3.4 billion barrels of of oil equivalent in the Permian Basin, a region that has drawn a flurry of land deals since last summer.

The companies have about 275,000 acres, about 90 percent of which is in the Permian, that produce 18,000 barrels of oil equivalent a day. The highly productive region has an estimated resource of 3.4 billion barrels of oil equivalent..

Exxon Mobil didn’t say, apart from BOPCO, which private companies it agreed to purchase.

“The acquisition strengthens Exxon Mobil’s significant presence in the dominant U.S. growth area for onshore oil production,” company Chairman and CEO Darren W. Woods said in a statement.