Brent and U.S. crude oil rallied more than $2 per barrel to multi-month highs on Monday. The lift comes from rising tension in Ukraine after Russian President Vladimir Putin declared he had the right to invade the country.
Russia is the world's biggest oil producer and so the move will undoubtedly affect the market.
Brent crude hit a session peak of $111.24 per barrel, its highest since January 2, and was up $1.48 at $110.55 by 0208 GMT.
U.S. crude futures jumped as much as $2.06 to $104.65 a barrel, the highest since September 23. They were later up $1.20 at $103.80.
Oil markets are reacting to the speculation and potential that the situation in Russian could worsen, although fundamental impact on oil markets is unlikely.