Graham Bull has succeeded Martin Durham as non-exec director after Bull stepped down, revealed Union Jack Oil (LON:UJO).
Durham has accepted a role with a joint venture partner and competitor and there is potential for conflicts of interest, the firm said.
Bull, 68, is a geologist with 46 years' experience and held positions with Chevron, Dome Petroleum, Siebens Oil and Gas and Poco Petroleum.
David Bramhill, Union Jack's executive chairman, said: "It is the good fortune of Union Jack to have secured the services of Graham Bull to succeed Martin as a non-executive director.
"Graham was instrumental in introducing two ventures, both resulting in discoveries to OilQuest Resources plc, a company founded by Joe O`Farrell and myself in the mid 2000's.
"Graham has already played an important part in the formation of Union Jack's current exploration portfolio including the introduction of the Wressle project to Union Jack. We welcome Graham to the team and look forward to him utilising his immense experience in helping to bring new ventures to the company".
Union Jack shares rose 2.78% to 0.37p.