At 2:40 pm (0640 GMT) New York's main contract, light sweet crude for November delivery, was down 48 cents to 60.07 dollars a barrel from 60.55 dollars in late US trades Friday.
The contract hit 59.95 dollars earlier Monday.
Brent North Sea crude for November was down 53 cents at 59.
88 dollars.
"A lot is going on that is increasing downward pressure on prices," said Dariusz Kowalczyk, senior investment strategist with CFC Seymor in Hong Kong.
He said the crude price was "struggling" at 60 dollars and could be expected to settle below that key level at some point during the week, if not later Monday in London or New York.
"The 60-dollar level is psychologically very important," Kowalczyk said.
"The market is looking scary ... it's falling like crazy and people are bailing out of their positions," said Tony Nunan, the manager for energy risk management at Mitsubishi Corporation in Tokyo.
"The market seems to be bearish with the Iran situation looking like it's reaching a co