New York's main contract, light sweet crude for delivery in December, shed three cents to $85.62 a barrel while Brent North Sea crude for December delivery fell eight cents to $107.65.
"Volumes remained low ahead of the presidential elections... and China's change in leadership," IG Markets said in a report.
"Instead of the usual Monday flurry, markets were decidedly quiet as no one wanted to take any big bets ahead of the race for the White House, which remains on a knife-edge."
US voters head to the polls later Tuesday with the race between President Barack Obama and Republican challenger Mitt Romney too tight to call, although Obama holds a slight edge in crucial swing states.
In China, Communist Party politicians were gearing up for a once-in-a-decade leadership change scheduled to take place at a Party congress, which starts on Thursday.