Brent crude for February delivery fell as low as $46.40 per barrel -- the lowest since March 2009 -- and US benchmark West Texas Intermediate (WTI) for the same month hit a similar trough at $44.20 a barrel.
"Today a Saudi official reiterated the belief ... that the days of $100 oil are over," said analyst Daniel Sugarman at traders ETX Capital.
"It is unclear whether this is truly what is felt in the corridors of power in Riyadh, or just something intended to stress the firm resolve of OPEC’s leading member not to back down from its stance of no output reduction."
Global oil prices have slumped by almost 60 percent since June, as the market faced abundant supplies, demand fears and a strong dollar in a stuttering global economy.
The slide accelerated in November when the Organisation of Petroleum Exporting Countries maintained its production ceiling at 30 million barrels per day.
Venezuela, which wanted OPEC to cut production, on Tuesday saw Moody's slash the country's debt rating by two notches to "Caa3" saying its lost oil revenues had "clearly increased" the risk of bankruptcy.