Global oil benchmark Brent crude plunged to its cheapest in almost 18 years on Monday and U.S. crude briefly tumbled below $20 per barrel on growing fears the global coronavirus shutdown could last months and demand for fuel will decline further.

With Saudi Arabia and Russia set to flood the market with oil next month, producers and shippers have been scrambling to lock oil up in storage as demand falls.

Meanwhile, the coronavirus pandemic is expected to cause at least a 20% drop in fuel demand worldwide as governments take steps to restrict the spread of the virus.

Brent futures fell $2.17, or 8.7%, to settle at $22.76 a barrel, their lowest close since November 2002, while U.S. West Texas Intermediate (WTI) crude fell $1.42, or 6.6%, to $20.09, the lowest close since February 2002.

The price war between Saudi Arabia and Russia erupted earlier this month after the collapse of a three-year deal to limit supply between the Organization of the Petroleum Exporting Countries (OPEC) and other producers led by Moscow.

So far, efforts at negotiation between the two producers and the United States have not changed the outlook. Saudi Arabia said on Monday it plans to boost oil exports to 10.6 million barrels per day (bpd) from May.

U.S. President Donald Trump and Russian President Vladimir Putin agreed during a phone call to have their top energy officials meet to discuss slumping global oil markets.

Major crude benchmarks have recorded losses for five straight weeks. The price of oil is now so low that it is becoming unprofitable for many oil firms to remain active, analysts said, and higher-cost producers will have no choice but to shut production, especially since storage capacities are almost full.

The market added to earlier losses after traders said Genscape reported that U.S. stockpiles at the key Cushing storage hub in Oklahoma rose more than 4 million barrels last week, which was the biggest-one week increase in more than 10 years.

Declining demand and expectation that storage will be swiftly filled has squeezed prices for major U.S. grades of crude oil, including crude traded out of Midland, Texas, the heart of U.S. shale production, which now trades at roughly $10.75 a barrel - a steep discount to WTI, and one that suggests heavy oversupply to come.

Bank of America lowered its oil price forecasts for the second time in two weeks after the bank's economists projected global GDP would contract in the first half of 2020.

"On a quarterly basis, we expect to see the steepest decline in global oil consumption ever recorded," BofA analysts said, reflecting a 12 million bpd drop in the second quarter of 2020 and a 4.5 million-bpd contraction for the year.

BofA reduced its 2020 price forecasts to $37 per barrel for Brent and $32 for WTI and said it expects both benchmarks will trade in the teens in coming weeks.

Rystad Energy's head of oil markets, Bjornar Tonhaugen, said: "The oil market supply chains are broken due to the unbelievably large losses in oil demand, forcing all available alternatives of supply chain adjustments to take place during April and May."

These included cutting refinery runs and increasing onshore or offshore storage, he said.

Supertanker freight rates are rising for a second time this month as traders rush to secure ships for storage.

Goldman Sachs analysts said demand from commuters and airlines, which account for about 16 million bpd of global consumption, may never return to previous levels.