Shell’s two biggest oil discoveries offshore Namibia — Jonker and Graff — would appear hold less recoverable reserves than was estimated last summer, according to a top executive within the Ministry of Mines & Energy.

Last August, Shiwana Ndeunyema, acting managing director of state oil company Namcor, told a conference in Windhoek that 11 billion barrels of oil-in-place had been discovered in the prolific Orange basin.