An investigation was carried out to evaluate the corrosion behaviour of carbon steel in deaerated 1.0M NaCl solutions and artificial seawater at pH ranges of 3 to 8.5 and temperatures up to 80 degrees C under static conditions using the polarization resistance technique. The effect of scale inhibitor addition on the corrosion rates was also studied. It has been found that the polarization resistance of carbon steel in deaerated solutions is generally high. With increasing pH, the polarization resistance increases, and is highest at 25 degrees C and lowest at 80 degrees C. In long-run measurements, for 50 degrees C at pH 8.5 the corrosion rates gave lower values compared to short-run measurements under the same conditions. This reduction in the corrosion rate is due to the formation of a protective hydroxide film on the metal surface, which restrict access of H2O to the surface. The results obtained with addition of 20 ppm phosphonobutanetri-carboxylic-acid scale-inhibitor at 50 degrees C at pH 8.5 showed that there was no effect on the R-P values.