Rotterdam, the largest port in Europe, is running out of space to store crude oil as plunging demand for fuel triggers a global supply glut.

Some oil tankers have been forced to drop anchor outside the Dutch port and others are being diverted elsewhere, according to Royal Dirkzwager, one of the harbour's management companies.

Rotterdam, one of the world's largest petrochemical sites, has a refinery and a sprawling “tank farm”, where about 75 million barrels of crude oil or refined products, such as petrol and diesel, can be stored before processing or onward shipment. But with global oil consumption set for its biggest fall in 25 years this year and last, most of the available capacity appears to be in use.

“There is no space at the terminals,” Jeroen Kortsmit, manager for commercial affairs at Royal Dirkzwager, said. “It's the fullest I have seen in my [24-year] career. There are a lot of vessels at anchor and some are being diverted.”

This growing global “oil lake” is a key factor depressing oil prices, Richard Savage, head of energy research for Mirabaud, the Swiss bank, said. The economic downturn has destroyed demand, sending the price of crude plummeting from a record high of $147 a barrel in July 2008 to $51.63 on Friday.

In addition to onshore storage facilities such as those at Rotterdam, about 100million barrels of crude are being hoarded at sea aboard supertankers, according to Jens Martin Jensen, acting chief executive of Frontline, the world's largest tanker company. With total UK demand standing at 1.7million barrels a day, that would be enough to supply Britain's oil needs for 59 days.

Mr Jensen said that 50 VLCCs (very large crude carriers), each carrying about two million barrels of crude, were being used for offshore storage in Europe, Asia, West Africa and the Gulf of Mexico. Up to 20 of these are believed to be in the Rotterdam-Amsterdam area. Globally, another 40 smaller vessels are thought to be carrying another 25 million barrels of refined products, such as heating oil.

The total volume of crude being stored at sea is changing constantly, but has risen to the present record levels because the price of oil for immediate delivery stands well below the value of oil for future consumption - a market phenomenon known as a contango. This has created a lucrative trading opportunity for oil companies, which can arbitrage between the different prices on the spot and futures markets.

Mr Savage said that the “relentless build in crude stocks” was creating a drag on prices, which he said could slide farther in the months ahead.

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