WTI for January delivery settled down $1.90, or 3.3%, to $55.91 a barrel on the New York Mercantile Exchange, the lowest level since May 5, 2009.
Brent, the global benchmark, fell 79 cents, or 1.3%, to $61.06 a barrel on ICE Futures Europe, the lowest settlement since July 2009.
Oil prices have been sliding for months and continue to decline near the year's end as OPEC pledged to maintain production despite a global oversupply. The organization has said cutting output would have little effect on price and would only lead to a surrender of some market share, according to CNBC.
Separately, European Union competition authorities gave conditional clearance on Monday for oil major BP to acquire jet fuel business Statoil Fuel and Retail Aviation, Reuters reports.
TheStreet Ratings team rates BP PLC as a Hold with a ratings score of C+. TheStreet Ratings Team has this to say about their recommendation:
"We rate BP PLC (BP) a HOLD. The primary factors that have impacted our rating are mixed - some indicating strength, some showing weaknesses, with little evidence to justify the expectation of either a positive or negative performance for this stock relative to most other stocks. The company's strengths can be seen in multiple areas, such as its reasonable valuation levels, good cash flow from operations and largely solid financial position with reasonable debt levels by most measures. However, as a counter to these strengths, we also find weaknesses including deteriorating net income, disappointing return on equity and poor profit margins."