Tony Hayward, the former BP chief, is snubbing corporate governance rules by stepping up to become chairman of FTSE 250 oil producer Genel Energy.
Hayward — who is also chair of commodities giant Glencore — has been chief executive of the company that he founded in 2011 with financier Nat Rothschild.
His promotion follows chairman Rodney Chase’s departure after four years leading the board.
City rules do not explicitly prevent chief executives from becoming chairmen, but they do discourage it.
He is replaced as chief executive by Murat Ozgul, currently head of Genel’s operations in its core business in Turkey and Kurdistan.
Five years ago Ozgul was fined £105,240 by the Financial Services Authority for insider trading in London-listed Heritage Oil.
At the time the FSA said it recognised he had not set out to “commit market abuse”.
The incident came to light when Ozgul voluntarily confessed to the FSA, with two colleagues.
Genel said volumes had grown rapidly in the first half — rising 41% year on year — with more than 100,000 barrels of oil produced on peak days.
