Brent crude, the international benchmark, also slumped, but that contract was nowhere near as weak because more storage is available worldwide.
While US oil prices are trading in negative territory for the first time ever, it is unclear whether that will trickle down to consumers, who typically see lower oil prices translate into cheaper petrol at the pump.
As billions of people around the globe stay home to slow the spread of the novel coronavirus, physical demand for crude has dried up, creating a global supply glut.
US traders fled from the expiring May US oil futures contract in a frenzy on Monday with no place to put the crude, but the June WTI contract settled at a much higher level of $US20.43 a barrel.
John Kilduff, partner at hedge fund Again Capital in New York, said normally such a situation would stimulate the global economy.
“It normally would be good for an extra two per cent on the GDP. You’re not seeing the savings because no one is spending on the fuels,” he said.
The May US WTI contract fell $US55.90, or 306 per cent, to settle at a discount of $US37.63 a barrel after touching an all-time low of -$US40.32 a barrel.
Brent was down $US2.51, or nine per cent, to settle at $US25.57 a barrel.
Louise Dickson, oil markets analyst at Rystad Energy, said “it’s like trying to explain something that is unprecedented and seemingly unreal”.
“Pricey shut-ins or even bankruptcies could now be cheaper for some operators, instead of paying tens of dollars to get rid of what they produce.”
Refiners are processing much less crude than normal, so hundreds of millions of barrels have gushed into storage facilities worldwide.
Traders have hired vessels just to anchor them and fill them with the excess oil. A record 160 million barrels is sitting in tankers around the world.
US crude stockpiles at Cushing rose nine per cent in the week to April 17, totalling around 61 million barrels, market analysts said, citing a Monday report from Genscape.
The spread between May and June at one point widened to $US60.76, the widest in history for the two nearest monthly contracts.
Prices have been pressured for weeks with the coronavirus outbreak hammering demand while Saudi Arabia and Russia fought a price war and pumped more.
The two sides agreed more than a week ago to cut supply by 9.7 million barrels per day (bpd), but that will not quickly reduce the global glut.
Brent oil prices have collapsed around 60 per cent since the start of the year, while US crude futures have fallen around 130 per cent to levels well below break-even costs necessary for many shale drillers.
This has led to drilling halts and drastic spending cuts.
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