Bioremediation has been recognized as an effective method to treat petroleum hydrocarbon pollutants. However, the biodegradation of crude oil-contaminated sludge could be a time-consuming and low-efficiency process. Among the reasons is that some petroleum hydrocarbons in the sludge are unavailable for micro-organisms' utilization. Surfactants have the potential to increase the bioavailability of such pollutants because of their capability to reduce the surface and interfacial tension and increase the solubility of hydrocarbons in water. In this study, the addition of two different chemical surfactants (Igepal CO-630 and Cedephos FA-600) were tested using a laboratory respirometer, and the effects of such surfactants on the biodegradation of total petroleum hydrocarbon (TPH) in the oil refinery sludge were investigated. Both surfactants have been found to be effective on improving microbial growth at low-concentration additions, while the concentration of 400 mg/kg has been found most effective for improving TPH (C10-050) reduction after 14 days of biodegradation.