US benchmark West Texas Intermediate for August delivery was down five cents to $100.86 while Brent crude for August eased 23 cents to $106.75 in afternoon trade.

US Federal Reserve chair Janet Yellen will begin two days of testimony later Tuesday before congressional committees that will focus on the bank's time-frame for raising benchmark interest rates.

French lender Credit Agricole said Yellen is likely to say that the Fed's key policy-making committee "look for the rate lift-off in 2015".

However, she will "emphasise that Fed views on the timing of the lift-off remain contingent on the economic outlook", the bank said in a market commentary.

Oil prices remain supported following turmoil in Libya, which has clouded expectations of a return of the country's long-disrupted crude supplies to the market.

Libya suspended all flights to and from its third city Misrata on Monday, a day after deadly clashes closed the country's main international airport in Tripoli and damaged several planes.

Libya's interim Prime Minister Abdullah Al-Thani declared earlier this month that authorities had regained control of two export terminals -- Ras Lanuf and Al-Sidra -- blockaded by rebels demanding autonomy in the country's eastern region.

Crude futures had fallen heavily last week, stoked by the prospect that the ports could add about 500,000 barrels of crude per day to global energy markets.

The North African state's output currently stands at about 320,000 barrels per day, about a fifth of its normal output.