Exxon Mobil Corp. plans to lay off 397 employees from Pioneer Natural Resources Co. after purchasing the Permian Basin operator for $63 billion earlier this year.

ExxonMobil Corp. warned that low energy prices may wipe as much as one-fifth of its oil and natural gas reserves off the books.

Exxon Mobil Corp. and Saudi Arabia’s state-controlled petrochemicals company formally approved construction of a chemical complex in Texas that will process production from the Permian Basin’s booming oil and natural gas wells.