Brent, the London-traded global benchmark for crude, settled down $1.08, or 2 percent, at $51.73 per barrel on Thursday. Brent fell to $50.39 during the session, its lowest since August 2017.
West Texas Intermediate (WTI), the New York-traded benchmark for US crude, closed down $1.64, or 3.4 percent, at $47.09 per barrel. WTI earlier fell to $45.88, its lowest since January 2019.
The US Energy Information Administration said earlier this week that it expects worldwide demand growth for oil to fall by 310,000 barrels per day this year due to the impact of the coronavirus.
Other forecasters have been more pessimistic. FG Energy said in a tweet that it envisaged zero growth in demand for 2020 as crude consumption suffers from a virtual freeze in business and activity in many parts of the world, especially China, due to the pandemic.
With Thursday's drop, Brent and WTI have lost about 13 percent each over five days of selling. Both crude benchmarks are down more than 20 percent on the year, pushing them into bear market territory.
Thursday's losses in oil came amid a brutal selloff on the US stock market too, where the broad Dow Jones index lost almost 1,200 points, while the S&P500, which reflects the top 500 US stocks, headed for its worst weekly drop since the financial crisis.
The Organisation of the Petroleum Exporting Countries and its allies, including Russia, are scheduled to meet in Vienna on 6 March to determine the intervention needed to stop the rout in oil. The group had earlier suggested a production cut of 600,000 barrels per day, or 0.6 percent of world demand, although it is far from certain if that will be adequate to save the market.