The price of US oil has fallen to a level not seen since 1999, as demand dries up and storage runs out.
The price of a barrel of West Texas Intermediate (WTI), the benchmark for US oil, dropped 19.3% to $14.74 a barrel on Monday.
The oil market has come under intense pressure during the coronavirus pandemic with a huge slump in demand.
US storage facilities are now struggling to cope with the glut of oil, weakening prices further.
The oil industry has been struggling with both tumbling demand and in-fighting among producers about reducing output.
Earlier this month, Opec members and its allies finally agreed a record deal to slash global output by about 10%. The deal was the largest cut in oil production ever to have been agreed.
But some analysts said the cuts were not big enough to make a difference.
"It hasn't taken long for the market to recognise that the Opec+ deal will not, in its present form, be enough to balance oil markets," said Stephen Innes, chief global market strategist at Axicorp.