Oil slid more than 5% at its session low on Monday, falling into bear market territory as the number of coronavirus cases outside of China surged.

Investors are worried that a subsequent slowdown in the global economy could dent the demand for crude.

U.S. West Texas Intermediate crude shed 3.65%, or $1.95, to settle at $51.43 per barrel for its worst day since Jan. 8, while International benchmark Brent crude fell $2.20, or 3.8%, to settle at $56.30 per barrel. At the session low WTI fell to $50.45, while Brent traded as low as $55.13.

Prices closed off the lows after Saudi Aramco CEO Amin Nasser reportedly said that the coronavirus impact will be "short term," according to a report from Reuters.

Again Capital's John Kilduff said that the $50 level is critical for energy companies. "This is it, this is the line in the sand. This is where they really start to hurt. This is where they start to not be able to service their debt, this is where the expense ratio does not work for Wall Street, for private equity, for anybody," he said Monday on CNBC's "Worldwide Exchange."