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.

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.

The size and scope of new U.S. sanctions on Russia sent oil prices spiking on Monday, and both Brent and WTI have retained most of those gains.

Oil prices climbed about 2% to a four-month high on Monday on expectations that wider U.S. sanctions on Russian oil would force buyers in India and China to seek other suppliers.

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 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.

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.