Catalytic reforming reaction of gamma-valerolactone (GVL) derived from renewable cellulosic biomass was conducted to produce hydrocarbon oils using a phosphoric acid catalyst under mild temperature (240 degrees C). Excellent catalytic performance (over 99% conversion of GVL, 33.5 wt% yield of hydrocarbon oils) was achieved in a one-step reaction without external source of hydrogen. The hydrocarbon oil formed was rich in aromatics and had similar C/H ratio and higher heating value (HHV) in comparison with oxygenated commercial gasoline.