Prices of oil fell on Monday to the lowest level since 2002, with WTI crude briefly falling below $20 a barrel.

The price of West Texas Intermediate, or WTI crude, fell 6.65 percent Monday morning, trading at around $20.09 by 10:30 a.m. The global benchmark Brent crude was down by around 10 percent to $22.39.

President Donald Trump said on Monday morning that he would talk to Russian President Vladimir Putin about oil supplies. A price war between Saudi Arabia and Russia is thought to be responsible for the recent steep decline in oil prices.

Oil prices are too low for many drillers to profitably extract oil from U.S. sites. Most oil market watchers believe prices need to be between $40 and $50 a barrel for U.S. extraction to break-even.

Gasoline prices in the U.S. have fallen to $1.97 on average, the lowest in decades.