Browne points out the Caspian Sea and Russia still boast large reserves

Lord Browne, the chief executive of the British oil giant BP, predicted prices would remain high in the near future.

But he said that large reserves still remained undiscovered or untapped, and that new technology would bring down extraction costs.

Sustained high oil prices have sparked fears of a global downturn.

"We cannot really count on oil prices easing very much in the near future," Lord Browne said in an interview with the German weekly Der Spiegel.

But he said in the medium term - the next five years or so - prices could average about $40 or so per barrel.

In the long term, the next decade or so, "it could even be $25 to $30".

Stark prediction

The BBC's Sumant Bhatia says some experts do expect oil prices to drop, but not nearly by the same margins as are being talked about here.

Lord Browne said large new oil fields are still being discovered, citing the Caspian Sea as an example. He said western Africa and Russia still had large reserves.

He added that technological developments meant the amount extracted from oil reserves could rise from the current 40% or 45%, to perhaps 50% or 60%.