Oil prices have fallen to levels not seen since 2004, surpassing the lows of the 2008 recession.
Brent crude sank to $US36.05 a barrel - its weakest since July 2004 - before recovering slightly to $US36.56.
Oil prices have slumped in the last 18 months. Photo: 123RF
A global oversupply has dramatically driven down the price of oil, with suppliers failing to reach agreements to address the glut.
A year earlier, the price of Brent stood at about $US60 a barrel. In June 2014, it stood at $US115.
The price of US crude was also down on Monday, dropping 40 cents to $US34.17 a barrel - the lowest since 2009.
Analysts and oil bosses have said there is little sign that the downward trend will change, with more US and Russian oil reaching the markets.
Iranian oil supply will also resume in 2016, following the lifting of sanctions.
In November, the 12 members of Opec maintained production at 30 million barrels per day, as first agreed in December 2011.
Many consumers have enjoyed the falling price of fuel in the form of lower petrol prices; several UK supermarkets have began selling petrol at below £1 per litre - which they last did in 2009.
However, oil firms have had profit margins squeezed, forcing them to cut spending in investment and exploration.
Governments of some oil producing countries have also been forced to cut spending as revenue from oil plunges.
The falling price has also led to questions about the merger of energy giants Royal Dutch Shell and BG Group.
Earlier this month, David Cumming, head of equities at Standard Life Investments, said the deal no longer "makes financial sense" with the oil price at current levels.
