Opec is staring down the barrel of a double cut

Brent crude fell 60 cents to settle at $51.81 a barrel, while U.S. West Texas Intermediate crude slipped 61 cents to settle at $50.18 a barrel.

Opec is going to have to do much more than simply extend its current production deal when it meets next week if it's serious about addressing surplus inventory. In fact, its own figures show it needs to double the cut it made in January.

That means finding a further 1.2 million barrels a day to take out of production.