Mr Hearne will move to a non-executive role, while Mike Pink is to retire as managing director after two-and-a-half years in the job. He is expected to receive a payoff not exceeding his annual salary of pounds 230,000.
The appointment of Mr Jungels, a Belgian, who starts the pounds 350,000-a-year post in January, sent shares in Enterprise 3.5p higher to 519p yesterday.
Mr Hearne is credited with building Enterprise into a major oil exploration and production group since its spin-off from British Gas in 1984, but he has not been popular with the City since the failure of his pounds 1.6bn bid for rival Lasmo two years ago.
One analyst said: "Graham Hearne fell out of favour during the bid for Lasmo, so quite a lot of people will be glad to see the back of him. There is a certain amount of relief that he is going." The 52-year-old Mr Jungels would be seen as a safe pair of hands, keeping the seat warm for the up and coming "young turks" among the junior management at Enterprise, he added.
Mr Hearne said it would be his 60th birthday next year, the normal date for retirement at Enterprise. "I wrote the rule book ... and I think it no bad thing to get a new chief executive after 13 years."
The board had been working on succession policy for some time and had always expected that Mr Pink, who also reaches retirement age next year, would bow out.
Mr Hearne said Mr Jungels would be "chief executive in every sense of the term", but he also said he intended to carry on as chairman for a few more years. Mr Jungels only joined British Gas at the end of last year, just before the group announced plans to break itself into two parts.Reuse content