Tullow Oil

Shares in the company have gained 90 per cent since the start of last year. Tullow's simple strategy - using cash thrown off by its mature but stable North Sea gas assets to take big punts on new wells - has borne fruit. Management, normally cautious in outlook and reserve estimates, now talks breathlessly of recent finds "transforming" the group's growth potential. Newly-struck wells in Ghana and Uganda could each more than double Tullow's current production output. And then there's Namibia, where the company looks well positioned to export gas to South Africa before long.

These three big engines give Tullow a more rounded portfolio than peers. Edinburgh's Cairn Energy, for example, has most of its chips on India while Soco International, based in London, has gone big on Vietnam. The promise of riches to come allowed the market to shrug off Tuesday's 56 per cent dip in first-half pre-tax profits, caused mostly by a fall in gas prices from last year's highs.

Membership of the UK's blue-chip index should give Tullow shares a further lift but at around 540p currently, the valuation still lags most estimates of net asset value. The longer it lags, the more vulnerable the company looks to a bid. Aidan Heavey, founder and chief executive, says he has no desire to sell. But if crude prices stay high, Heavey may find that Tullow's stay at the top table is short-lived.