Prince Abdulaziz bin Salman Al-Saud, Minister of Energy of Saudi Arabia arrives for the 178th meeting of the Organization of Petroleum Exporting Countries (OPEC) in Vienna, Austria, on March 6, 2020. Alex Halad | AFP | Getty Images

Oil prices plunged to multi-year lows on Monday as tensions between Russia and Saudi Arabia escalate, sparking fears on the Street that an all-out price war is imminent. The sell-off in crude began last week when OPEC failed to strike a deal with its allies, led by Russia, about oil production cuts. That, in turn, caused Saudi Arabia to slash its oil prices as it reportedly looks to ramp up production. U.S. West Texas Intermediate crude and international benchmark Brent crude on Monday posted their worst day since 1991. WTI plunged 24.59%, or $10.15, to settle at $31.13 per barrel. It was WTI's second worst day on record. International benchmark Brent crude slid $10.91, or 24.1%, to settle at $34.36 per barrel. Earlier in the session each contract fell more than 30%. WTI dropped to $30 while Brent traded as low as $31.02, both of which were the lowest levels since Feb. 2016.

"This has turned into a scorched Earth approach by Saudi Arabia, in particular, to deal with the problem of chronic overproduction," Again Capital's John Kilduff said. "The Saudis are the lowest cost producer by far. There is a reckoning ahead for all other producers, especially those companies operating in the U.S shale patch." On Saturday, Saudi Arabia announced massive discounts to its official selling prices for April, and the nation is reportedly preparing to increase its production above the 10 million barrel per day mark, according to a Reuters report. The kingdom currently pumps 9.7 million barrels per day, but has the capacity to ramp up to 12.5 million barrels per day.

"We believe the OPEC and Russia oil price war unequivocally started this weekend when Saudi Arabia aggressively cut the relative price at which it sells its crude by the most in at least 20 years," Goldman Sachs analyst Damien Courvalin said in a note to clients Sunday. "The prognosis for the oil market is even more dire than in November 2014, when such a price war last started, as it comes to a head with the significant collapse in oil demand due to the coronavirus," the firm added. Goldman cut its second and third quarter Brent forecast to $30 per barrel, and said that prices could dip into the $20s. Saudi Arabia's price cut followed a breakdown of talks in Vienna last week. On Thursday, OPEC recommended additional production cuts of 1.5 million barrels per day starting in April and extending until the end of the year. But OPEC ally Russia rejected the additional cuts when the 13-member cartel and its allies, known as OPEC+, met on Friday.

The meeting also concluded with no directive about the production cuts that are currently in place but set to expire at the end of the month. This effectively means that nations will soon have free rein over how much they pump. "As from 1 April we are starting to work without minding the quotas or reductions which were in place earlier," Russian Energy Minister Alexander Novak told reporters Friday at the OPEC+ meeting in Vienna, adding, "but this does not mean that each country would not monitor and analyze market developments." Oil prices have already moved sharply lower this year as the coronavirus outbreak has led to softer demand for crude. A potential supply glut could pressure prices further.