Oil prices have continued their downward spiral this week after US President Donald Trump urged Saudi Arabia and OPEC not to cut their production.
Taking to Twitter on Monday, Trump said: "Hopefully, Saudi Arabia and OPEC will not be cutting oil production. Oil prices should be much lower based on supply!"
The comments caused West Texas Intermediate (WTI) to fall 7% to $55.7 a barrel, its largest one-day drop since September 2015, while Brent Crude suffered its twelfth consecutive drop on Tuesday, falling 6.6% to $65.5 a barrel.
This means both benchmarks have now declined more than 25% since last month and are now in a bear market - defined as a 20% drop from a recent high.
Trump's comments came after Saudi Arabia's energy minister Khalid Al-Falih said the kingdom's output would drop by 500,000 barrels per day (bpd) in December in an attempt to halt the dramatic fall in prices.
Speaking at a conference in Abu Dhabi, Al-Falih said: "The consensus among all members is that we need to do whatever it takes to balance the market. If that means trimming supply by a million bpd we will do it."
Prices were further impacted after the research arm of OPEC on Tuesday forecasted oil demand growth to increase by 1.29m bpd, 70,000 barrels lower than its prior forecast and down from the 1.45m bpd predicted in July.
Joshua Mahony, market analyst at IG, commented: "Recent claims from the IEA that 2019 will see a widening gap between the supply and demand have been reiterated by OPEC, and the prospect of a glut of oil in the following months is helping drive oil into a seven-month low.
"The knowledge of a potential major oversupply has been enough to push Saudi Arabia to take steps to reduce their output.
"However, the fact that markets are willing to look straight past a 500,000 bpd production cut highlights the fact that it is going to take some serious action from OPEC to arrest a potential drawn out sell-off in oil prices."
The fall comes after oil prices were trading around $80 a barrel as recently as October amid a number of supply issues including sanctions on Iran, political turmoil in Venezuela and tightening supply from OPEC.