Brent crude fell to $22.58 (£18.19) a barrel at one point on Monday, its lowest level since November 2002.
Meanwhile the price of US West Texas Intermediate (WTI) fell below $20 a barrel and close to an 18-year low.
Oil prices have fallen by more than half during the past month as companies cut back or close production.
In addition to the drop in demand, a price war broke out earlier this month between Saudi Arabia and Russia.
This began when Saudi Arabia failed to convince Russia to back production cuts that had been agreed with the other members of the Opec oil producers' group.
The decision came as refineries around the world are processing less crude oil. Demand for transport has been hammered by grounded airlines and fewer cars on the roads as countries bring in tougher measures to fight the coronavirus outbreak.
However, an analyst said a collapse in demand from the measures taken to counter the spread of coronavirus was now the main factor.
