Associated Press

Oil prices slumped the most since 1991 after Saudi Arabia's weekend price cuts sparked a race to the bottom between OPEC, Russia, and the US.

Brent crude futures sank as much as 31% to $31.02 per barrel Monday morning, while West Texas Intermediate contracts tumbled as much as 34% to $27.34 per barrel.

The new volatility in oil markets "completely changes the outlook" and could see Brent crude sink as low as $20 per barrel in 2020, Goldman Sachs analysts wrote.

Watch Brent crude trade live here.

Oil prices tanked the most since 1991 in early Monday trading after Saudi Arabia slashed prices and prompted retaliation from Russia.

Demand for the commodity has plummeted since the coronavirus began tearing into the global travel and tourism industries, leaving the Organization of Petroleum Exporting Countries racing to support the ailing sector. Russia refused OPEC's plan to slash production and support the market, driving the price of Brent crude down nearly 10% on Friday to $45.27 per barrel.

Saudi Arabia fired back on Saturday, cutting its prices the most in 20 years and sparking a price war between OPEC, Russia, and the US. The fallout pushed Brent crude futures down as much as 31% to $31.02 per barrel on Monday morning, its second-biggest drop since the Gulf War in 1991.

West Texas Intermediate futures sank as much as 34% to $27.34 per barrel.

Read more: 'Much worse than 2008': An expert who foresaw the dot-com crash warns the stock market's recent turmoil has kicked off another full-blown financial crisis

Prices for both oil classes partially recovered through the morning. Brent traded down 22% to $35.30 per barrel as of 9:20 a.m. ET. WTI was down 22% to $32.12 per barrel.

"This completely changes the outlook for the oil and gas markets, in our view, and brings back the playbook of the New Oil Order, with low cost producers increasing supply from their spare capacity to force higher cost producers to reduce output," Goldman Sachs analysts wrote Sunday.

The bank lowered its second- and third-quarter Brent forecasts to $30 per barrel, adding that potential price drops could even see the commodity sink to $20 per barrel.

The oil pricing chaos drove fresh volatility across other markets. Stock market futures tumbled before the open, and yields for all US Treasury bills dipped below 1% for the first time ever.

Now read more markets coverage from Markets Insider and Business Insider:

Stocks are fresh off their most chaotic week since 2011. Here's why the market is so confused about what's next.

Billionaire investor Steve Cohen is reportedly raising money for a new fund designed to invest in private companies

BANK OF AMERICA: These 5 metrics will determine the length and severity of a coronavirus-fueled recession

Markets Insider

NOW WATCH: A big-money investor in juggernauts like Facebook and Netflix breaks down the '3rd wave' firms that are leading the next round of tech disruption