The effect of N-propyl amino lauryl amide (1) and three of its ethoxylated derivatives (II, III and IV) as corrosion inhibitors of carbon steel in I M hydrochloric acid solution has been studied by weight loss and galvanostatic polarization techniques. A significant decrease in the corrosion rate of carbon steel was observed in the presence of the investigated inhibitors. The study revealed that, the inhibition efficiency (I, %) increases with increasing the inhibitors concentration. All the tackled inhibitors seem to have obeyed the Langmuir adsorption isotherm. The galvanostatic polarization data indicated that, the inhibitors were of mixed type, but the cathodic effect is more pronounced. The slopes of the cathodic and anodic Tafel lines are approximately constant and independent on the inhibitor concentration. The relation between the surface tension of the inhibitor (gamma) and the logarithm of their concentrations (log C) was investigated to obtain the adsorption ability of the inhibitors on the carbon steel surface. Scanning electron microscopy was used to examine the surface morphology of the carbon steel specimens after immersion in 1 M HCl for 6 days in absence and presence of 500 ppm of the inhibitor IV. The mechanism of inhibition was discussed in the light of the chemical structure of the undertaken inhibitors. (C) 2002 Elsevier Science B.V. All rights reserved.