Investor optimism that the ECB could take action to ease Spanish and Italian borrowing costs remained, even though on Monday the central bank sought to quell speculation contained in a report suggesting it was considering buying bonds of euro zone countries if their borrowing costs breached a certain level.

U.S. front-month September crude futures hit a three-month high above $97 a barrel, with the contract set to expire at the end of the session.

An upcoming maintenance-related North Sea oil production slide and heightened tensions in the Middle East as violence in Syria continues and Iran's dispute with the West over Tehran's nuclear program added to the lift for oil prices.

Brent's sensitivity to North Sea production curbs and the Middle East turmoil has kept front-month contracts priced above months further out, or in backwardation, and provided the lift to bring prices back well above $100 a barrel after settling at $89.23 on June 21.

On Tuesday, Brent October crude rose $1 to $114.70 a barrel at 12:54 p.m. EDT (1654 GMT), having reached $115.58.

Brent hit a three-month peak at $117.03 last Thursday as its September contract headed to expiration and went off the board at $116.90 a barrel, the highest settlement since May 2.

U.S. September crude was up $1.05 at $97.25 a barrel, having hit $97.60, the highest price since front-month crude reached $97.69 intraday on May 10.

U.S. October crude was up $1 at $97.26 a barrel.

"Optimism for a breakthrough in dealing with Greece is propelling the risk appetite," Addison Armstrong, senior director for market research at Tradition Energy said in a note.

Greek Prime Minister Antonis Samaras will meet German Chancellor Angela Merkel, French President Francois Hollande and Eurogroup chief Jean-Claude Juncker this week to try to secure more funding from the European Union, International Monetary Fund and ECB, despite falling behind on its targets to cut debt.

U.S. gasoline and heating oil also rallied around 1 percent as recent refinery problems keep supporting fuel prices.

Price strength for U.S. oil futures also came from concerns about tropical weather threats, with Tropical Depression Nine headed west toward the Caribbean.

Another low pressure system in the Atlantic is expected to become a tropical cyclone in the next two days, the U.S. National Hurricane Center said.

Weekly reports on U.S. oil inventories are expected to show crude stocks edged up slightly last week, by 100,000 barrels, a Reuters survey of analysts on Monday showed.

Distillate stocks are expected to be up 1.3 million barrels, with gasoline inventories near flat, slipping 100,000 barrels.

MIDDLE EAST TURMOIL

Turkey is investigating possible Syrian links to Monday's deadly car bomb attack near its southeastern border, officials said, highlighting concerns that the conflict might start to spill out of Syria's borders.

Russian Foreign Minister Sergei Lavrov met China's top diplomat and a Syrian government delegation on Tuesday, a day after President Barack Obama said U.S. forces could intervene if Syrian President Bashar al-Assad deployed chemical weapons against rebels trying to topple him.

The U.N. nuclear agency and Iran are expected to meet on Friday for the first time since a June meeting produced no progress towards answering questions about suspected nuclear weapon research in the Islamic state, according to diplomats.

The U.N.'s International Atomic Energy Agency (IAEA) declined to comment on whether a new meeting was planned and there was no immediate comment from Iran's diplomatic mission in Vienna.