(Reuters) — Royal Dutch Shell plc’s head of crude oil trading Mike Muller, has stepped down after 29 years with the company, an internal announcement reviewed by Reuters on Friday showed.

Muller, one of the world's most powerful oil traders, has relinquished his role with immediate effect and will leave at the end of the year "to pursue interests outside of Shell."

His departure follows the appointment of Andrew Smith as Shell's new head of supply and trading earlier this year.

Mark Quartermain, currently head of refined products trading, has been appointed vice-president trading and supply crude with effect from Dec. 1.

Under Muller, a Cambridge university graduate, Shell expanded trading aggressively, handling as much as eight million bbls/d and often taking large position in core markets such as the North Sea, home to benchmark crude Brent.

Smith recently said trading was Shell's "nerve centre" as it shifts millions of bbls of crude and refined products from fields to its refineries and consumers.

Though Shell does not disclose separately its revenue from supply trading, they often help offset declines in crude oil production when oil prices slump, as has been the case over the past three years, by making profits from price volatility and supply disruptions.

Shell, the world's second largest publicly-traded oil company, traded more oil than any of its top rivals such as BP plc or trading houses Vitol or Glencore.

Shell also helped Mexico hedge its oil output for 2017 and in 2018 become the first oil major to join the program, which has usually been dominated by big Wall Street banks.