The effect of temperature and organic loading rate on the rate of methane production from acidic petrochemical wastewater without neutralization was investigated by continuously feeding an anaerobic upflow fixed-film reactor. The temperatures selected for the studies were 25, 37, 45 and 55 o C. Organic loading rate (OLR) for each temperature was varied from 3.6 to 21.7 kg COD m - 3 d - 1 . Best performance with respect to COD and BOD reduction, total gas production and methane yield was obtained with the reactor operating at 37 o C. OLR could be increased to a maximum of 21.7 kg COD m - 3 d - 1 with 90-95% COD and BOD reduction and methane yield of 0.450 m 3 kg - 1 COD d - 1 added. The reactor operating at 55 o C gave the highest methane yield of 0.666m 3 kg - 1 COD d - 1 at an OLR of 6 kg COD m - 3 d - 1 . This decreased to 0.110 m 3 kg - 1 COD d - 1 when the OLR was increased to 18.1 kg COD m - 3 d - 1 . The reactor operating at 45 o C gave a maximum methane yield of 0.416m 3 kg - 1 COD d - 1 added at an OLR of 6 kg COD m - 3 d - 1 . On further increasing the OLR to 9 kg COD m - 3 d - 1 , COD reduction was 89%, however, methane yield decreased to 0.333m 3 kg - 1 COD d - 1 added. The highest methane yield of 0.333m 3 kg - 1 COD d - 1 added at an OLR of 6 kg COD m - 3 d - 1 was obtained with reactors operating at 25 o C. These studies indicate potential rates of methane production from acidic petrochemical wastewater under different temperatures. This provides a guideline for various kinetic analyses and economic evaluation of the potential feasibility of fermenting acidic wastewater to methane.