Oil prices were mixed in Asia today as investors await congressional testimony by the US central bank chief for fresh clues about the state of the world's biggest economy. US benchmark West Texas Intermediate for August delivery rose one cent to 100.92 Dollars while Brent crude for August eased 18 cents to 106.80 Dollars in late-morning trade. US Federal Reserve chair Janet Yellen will begin two days of testimony later today before congressional committees that will focus on the bank's time-frame for raising benchmarkinterest rates.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.