A non-ionic surfactant, octylphenol polyethylene oxide (OPPEO), was evaluated as an inhibitor for corrosion of low-carbon steel in 0.5 M H2SO4. Potentiodynamic and potentiostatic methods and scanning electron microscopy were used to study the inhibition effectiveness of the surfactant. The inhibition efficiency was found to increase with the inhibitor concentration and decrease with temperature. OPPEO showed higher constant protection efficiency near its critical micelle concentration. The activation energy of corrosion was found to be higher in presence than in absence of the inhibitor. The experimental data were fitted with the Flory-Huggins isotherm at a molecular ratio of 5:1. The Gibbs energy of adsorption decreases with the temperature. The inhibitor has relatively lower inhibition efficiencies at ambient and higher temperature. This was attributed to the molecular structure of the inhibitor. (C) 2004 Elsevier B.V. All rights reserved.