The share of the oil market claimed by producers' cartel Opec is at its lowest level since the mid-1980s, the International Energy Agency (IEA) has said.

Oil prices have fallen by a third since the 11 September attacks in the US.

Production cuts imposed since by Opec members to boost prices have left them with a smaller share of the oil market.

The world league of top-10 oil producers now contain just three Opec members, although the cartel still controls more than half of world exports.

"Opec's focus on price stabilisation and short-term revenue growth has contributed to a significant reduction in its market share," an IEA report said.

Lost market share?

The report added that successive output cuts will make it difficult for Opec to regain its lost market share.

"There is a number of uncertainties out there, the state of the economy, how quickly the economy is going to improve, how far it is going to improve, what is going to happen to oil demand," report author Klaus Rehag said.

The IEA is an arm of the Organisation for Economic Cooperation and Development (OECD).

It was set up in 1970s to protect the industrialised world from the cartel power of Opec.