Oil prices fell marginally on Friday as investors weighed optimistic demand forecasts from the OPEC producer group against mixed economic data in top importer China. Brent crude fell 15 cents to $86.25 a barrel at 0515 GMT, while U.S. West Texas Intermediate crude futures were down 13 cents at $82.69 a barrel. Both benchmarks have been on a sustained rally since June, with West Texas Intermediate crude (WTI) trading on Thursday at its highest this year and Brent hitting its best price since January. “Oil markets may have been overbought from a multi-week rally, though