Exxon Mobilis close to buying Pioneer Natural Resources (PXD.N) in a deal that could be worth about $60 billion, Reuters reported on Thursday.

The deal would be Exxon’s largest since it bought Mobil for $81 billion in 1998 and would boost its presence in one of the most profitable areas of the U.S. oil industry.

Pioneer, which had a market value of $50 billion as of Thursday, is the third-biggest oil producer in the Permian basin after Chevron Corp (CVX.N) and ConocoPhillips (COP.N). The Permian basin, which covers parts of Texas and New Mexico, is the most sought-after area for U.S. energy companies because it is relatively cheap to get oil and gas out of it.