New York's main contract, light sweet crude for delivery in July, fell 13 cents to $83.14 per barrel while Brent North Sea crude for August delivery gained 10 cents to $96.15.
Fears that Spain would require a bailout were reignited after the borrowing costs on its 10-year bonds topped 7.0 percent on Monday, the highest level since the birth of the euro in 1999.
"Spanish bond yields reached euro-era highs, reminding investors that the region's economy remains stressed," Phillip Futures said in a report.
Nick Trevethan, senior commodities strategist for ANZ Research, added: "The big weight hanging over the market is what's going on in Europe."
Traders were also eyeing a two-day G20 summit currently being held in Mexico for more leads to the market, he said.