EOG Resources Inc. (NYSE: EOG) has named Lloyd W. “Billy” Helms Jr. to replace Gary Thomas, who is set to retire by year-end 2018, as the company’s COO, according to a news release.

Helms last served as executive vice president of E&P, a role that is now held by Ezra Y. Yacob. Yacob was previously vice president and general manager of EOG’s Midland office.

The changes took effect Dec. 13, EOG said in a news release.

Thomas will continue serving as president of EOG, the company said, to allow for the gradual transition of his responsibilities. Thomas has worked for EOG for 39 years, having held responsibility for managing the company’s overall drilling, completions, production and engineering activities since 1998.

With a 36-year tenure with EOG, Helms has been responsible for the company’s operations in Midland, San Antonio and Artesia as well as EOG’s engineering, acquisition and business development functions, according to the release.

Yacob has 12 years of service with EOG and has managed EOG’s Permian Basin exploration and development activities since May 2014, the release said.