Brent Crude suffered its biggest financial slump in four years in London yesterday, testing the $80-a-barrel mark.

In June, Brent Crude hit $115 but since then the price has slumped by more than 30%. With a 15% decrease this month alone. The price for December settlement, the forward month contract, fell $1.88, or 1.5 per cent, yesterday to $80.46 a barrel.

Traders are braced for further falls today when the Energy Information Administration, the statistical unit of the US Department of Energy, pub-lishes its inventory update, which is expected to show that stockpiles rose by more than 250,000 barrels last week.

Falling crude prices have had little impact on shale oil drilling in the United States, with output from the largest shale fields showing no sign of slowing. Yet if prices fall much farther, production will become less viable because of the high cost of extraction.

Other factors weighing on the energy market include concerns that Opec appears unable to settle on a united plan to cut production that would stop the plunge in crude prices.

The oil producers’ cartel, which will meet in Vienna this month, supplied 31 million barrels a day last month, more than 3 per cent above its target of 30 million barrels, adding to global stockpiles when growth in the big oil consuming nations appears to be slowing. On Monday analysts at JP Morgan slashed its Brent price forecast for 2015 by $33 to $82 per barrel.

According to Opec’s own estimates its share of the global oil market could shrink to 37 per cent in 2017 from 40 per cent last year. That would be the lowest in more than 25 years and far below its peak of 54 per cent in 1973.

Meanwhile, the loading dates of at least four cargoes of Forties crude, the largest of the four North Sea streams that underpin the Brent oil benchmark, have been delayed amid lower-than-expected production. Fifty oilfields are connected to the Forties pipeline.