High temperature and high pressure immersion tests in an autoclave were employed to study the corrosion behaviour of X52 pipeline steel in aqueous solutions containing high concentrations of H 2 S. The corrosion products generated were characterised using scanning electron microscope, energy dispersive spectroscopy and X-ray diffraction. It was seen that at a constant H 2 S concentration of 22 g/l, the corrosion rate increased with increasing temperature up to 90uC, thereafter decreased at 120uC and slightly increased again at 140uC while the corrosion rate increased with H 2 S concentration at a temperature of 90uC. When the temperature and H 2 S concentration increased, the corrosion product converted from iron rich to sulphur rich products in the following sequence: mackinawiteRtroiliteRpyrrhotite, where the microstructure and stability of the corrosion products had an important effect on the corrosion rate. The corrosion film was formed through the combination of the outward diffusion of Fe 2z ions and the inward diffusion of H 2 S and HS 2 species.