Permian Resources Corp., a US oil producer named after the shale basin in which it operates, agreed to acquire Earthstone Energy Inc. for about $2 billion through an all-stock takeover.

It’s the latest deal for Will Hickey and James Walter, the 30-something co-chief executive officers of Midland, Texas-based Permian Resources who have built up the company into a major independent US shale operator through a series of mergers in recent years. Including debt, the deal has an enterprise value of about $4.5 billion, according to a statement Monday.

Takeovers have been crucial for US shale producers to grow over the last two years as many of the best drilling sites have been tapped.

Permian Resources and Earthstone operate a combined total of 11 drilling rigs, primarily focused on the Delaware Basin of West Texas and southern New Mexico. Permian plans to keep all of them running for now after the deal closes, bucking an industry trend to cut rigs after buying rivals. Permian Resources may add or cut a rig depending on commodity prices and costs, Hickey said during a call with analysts.

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Buying Earthstone will give Permian Resources a pro-forma production of about 300,000 barrels of oil equivalent per day, the companies said in the statement. The transaction is expected to close by year-end.

Earthstone shares gained as much as 18%, while Permian’s rose 2.5%.

Read More: Shale’s 30-Something Co-CEOs Eye 10% Permian Production Boost

(Updates with deal value, context, rig details and share price starting in the fourth paragraph)