Oil prices fell on Monday as talks stalled on a Greek debt deal needed to avoid a disastrous default, raising concerns about the region's economy and future demand.
Benchmark crude fell by 96 cents to $US96.88 per barrel in New York.
Brent crude rose 74 cents at $US115.32 per barrel in London.
Traders are worried that Greece's political leaders may not agree on new austerity measures necessary for more billions in international bailout loans.
Greece's prime minister is meeting on Monday with negotiators from the eurozone and the International Monetary Fund after no agreement was reached over the weekend.
Prices continued to slide after President Barack Obama ordered sanctions on Iran that will make it harder for the world's third-largest oil exporter to sell its crude to other countries. The sanctions have been expected for some time.
The US and other western nations are confronting Iran about its secretive nuclear program, which may be developing weapons. Europe plans to stop buying Iranian oil this summer. Iran has threatened to blockade the Persian Gulf to stop oil tankers, if the embargo goes into effect.
The sanctions imposed by the US and Europe on Iran are not designed to stop the flow of oil out of Iran, because that would raise global oil prices at a time when the global economy is struggling.
Instead the sanctions aim to make it more difficult for Iran to sell its oil through traditional banking routes. The West hopes that will force Iran to sell its oil at a discount, and reduce the oil revenue it uses to run its economy and to fund its nuclear program.
'It'll be harder for them to collect money when they sell oil,' PFGBest analyst Phil Flynn said.
Investors also will be closely watching a slew of corporate earnings reports this week for clues about the strength of the US and global economies. Walt Disney, Coca-Cola and Cisco Systems are scheduled to announce fourth quarter results.
In other energy trading, heating oil rose by four cents to $US3.15 per gallon and petroleum futures rose by about one cent to $US2.92 per gallon. Natural gas fell by two cents to $US2.48 per 1000 cubic feet.
