The efficacy of an electrocoagulation process (ECP) was evaluated for the treatment of petroleum-contaminated groundwater and quantified as the total petroleum hydrocarbon (TPH) removed. Various operating variables were examined for their effects on TPH removal; these variables included electrode materials (aluminum, iron, and steel), water pH (4 to 11), current density (2 to 18 mA/cm(2)), reaction time (2 to 60 min), aeration, and the mode of operation (batch and continuous). Batch experiments indicated that the maximum TPH removal was achieved using steel-iron as the anode-cathode electrode arrangement and a neutral pH level. The increase in current density from 2 to 18 mA/cm(2) at optimum electrode and pH conditions increased TPH removal from 71.7 to 95.1% during the ECP. The rate of TPH removal followed a pseudo-second-order reaction. Aeration increased the reaction constant of TPH removal from 0.477 to 0.078 L/g.min. Increasing the hydraulic retention time from 10 to 60 min in the continuous operation mode of the ECP led to an increase in the TPH removal from 67.2 to 93.4%. Therefore, batch and continuous experiments showed that the ECP could be efficient in eliminating TPH from water and thus may be a promising technique for treating petroleum-contaminated groundwater. (C) 2011 Elsevier B.V. All rights reserved.