In this paper the efficiency of Ti/RuO2 anode in degrading organic substances, present in wastewaters from petroleum industry, before their discharge or reuse was investigated. Results indicated that the Ti/RuO2 electrode can be an efficient alternative for treatment of those effluents. The COD (Chemical Oxygen Demand) removals, after 120 min of electrolysis, with a current density of 10 mA cm(-2), anodic area of 107 cm(2), flow rate of 0.54 mL s(-1) and at 25 degrees C, were above 96%, for effluent AF (After Flotation), with 712 mg L-1 COD, and 87% for effluent BF (Before Flotation), with 833 mg L-1 COD. An almost complete COD removal from both effluents was achieved when current density was increased from 10 to 30 mA cm(-2) with anodic area of 107 cm(2), flow rate of 0.54 mL s(-1) and at 25 degrees C. The increase of current density also favored a decrease of the electrolysis time necessary to achieve a complete COD removal from both effluents, BF and AF. However, current density increase also led to a higher specific energy consumption. For effluent BF, the cost of the energy necessary to achieve a complete COD removal in 60 min with a current density of 30 mA cm(-2) with anodic area of 107 cm(2), flow rate of 0.54 mL s(-1) and at 25 degrees C was around US$ 38/kg COD, while for effluent AF, the energy cost for total COD removal after 30 min of electrolysis at a current density of 30 mA cm(-2) was only US$ 28/kg COD. (C) 2013 Elsevier B.V. All rights reserved.