The chairman of the UK firm exploring oil at Horse Hill near Gatwick, known as the "Gatwick gusher", is stepping down.
David Lenigas is leaving UK Oil and Gas Investments (UKOG) where he will be replaced by chief executive Stephen Sanderson.
"It is my policy to step down from the boards of companies once I believe that they have reached a state of maturity where they require sector-experienced executive management to take over," said Lenigas, who will remain remain as a consultant at the firm for at least four months.
"The progress the company has made is a source of great satisfaction and I feel confident that this is the right time to hand over the reins to a respected oil executive with high credentials who I believe will continue to drive the company forward."
Shares in the Aim-listed company tumbled four per cent on the news.
Sanderson, who became chief at the start of the year, thanked Lenigas and was "delighted to be asked to lead the company into what I believe will be a very exciting and productive future".