Royal Dutch/Shell says enquiry has changed

Royal Dutch/Shell said that the informal enquiry by the US Securities and Exchange Commission into the recategorisation of its reserves has now become a formal non-public investigation.

The company is the world's third largest oil and gas group and had proved reserves of 15.6 billion barrels of oil equivalent.

Last month the oil giant said up to 3.9 billion barrels of oil equivalent of proved reserves have been "recategorised" following a review, leading to a cut in reserves.

They represent about 20% of the group's proved reserves.

Most of the oil giant's crude is produced in Nigeria, Oman, Britain, and the US.

Royal Dutch/Shell owns or has interests in about 50 refineries worldwide.