The inhibiting effect of 12-aminododecanoic acid (AA) on corrosion of carbon steel (CS) was investigated in hydrochloric acid of different pH, temperatures and over a prolonged period of time, and also in some other selected corrosive solutions. It was found that AA inhibits both partial corrosion reactions, with a slightly stronger inhibition of the anodic corrosion reaction. The corrosion protection mechanism is by formation of a surface-adsorbed AA monolayer that offers a hydrophobic barrier to transport of solvated corrosive ions to the surface. A maximum inhibition efficiency of 98.8 +/- 0.5% was achieved in 0.5 M HCl. The adsorption of AA onto the CS surface was described by the Langmuir adsorption isotherm. The corresponding standard Gibbs energy of adsorption was calculated to be -26 kJ mol(-1). Polarization modulation infrared reflection absorption spectroscopy measurements revealed that the adsorbed AA monolayer is amorphous, which is due to the high heterogeneity of the CS surface. (C) 2011 Elsevier Ltd. All rights reserved.