Oil futures were up strongly Monday, with Brent crude on track for its first finish above $80 a barrel since August, as investors assess the potential hit to supply from a further tightening of sanctions on Russia’s oil sector.

Crude oil prices surge as U.S. sanctions on Russian oil disrupt global supplies, driving Brent crude above $81/bbl to the highest in nearly five months.

Goldman Sachs is warning of potential upside risks to oil prices following U.S. sanctions on Russia's energy sector, with Brent crude already approaching $80 per barrel and the possibility of hitting $90 under certain scenarios.

Oil prices slipped on Tuesday from the previous day's four-month highs but the market remained supported by continuing focus on the impact of new U.S. sanctions on Russian oil exports to key buyers India and China.

Sweeping U.S. sanctions on Russia's oil industry will make it more expensive for Moscow to sell its oil and complicate sea-borne crude exports due to restrictions on tankers, analysts and traders said on Monday.

Oil prices paused their rally on Tuesday, but remained near four-month highs, with the market's attention focused on the impact of new U.S. sanctions on Russian oil exports to key buyers India and China.

At least 65 oil tankers have anchored in various locations around the world, including off the coasts of China and Russia, since the US announced a new package of sanctions on January 10, Reuters reports.