The recent developments of high pressure and sour wells in the North Sea area have increased the need for high strength H2S resistant carbon steels. Steel chemistry and heat treatment solutions have been available to provide products suitable for use in these environments within the constraints of classic well design since the early 90’s but operators are now demanding higher strength and heavier wall products for HPHT wells. Well completion design teams are now specifying from OCTG suppliers C 110 grade products in increasingly heavy wall and the challenge facing suppliers is to guarantee product integrity not only of these heavy wall casing but also the associated coupling stocks. This paper was aimed at evaluating the performances of thick walled C 110 tubulars (up to 2”) for sour environments. Metallurgical characteristics (microstructure, structure, microhardness), mechanical properties (hardness, tensile, toughness), Sulfide Stress Cracking resistance (smooth tensile, DCB) have been investigated throughout the wall thickness. The C 110 proprietary grade proved to be an excellent material for use as Oil Country Tubular Goods (OCTG) in typical North Sea environments with improved assessment of H2S corrosion resistance properties according to both NACE and EFC (European Federation of Corrosion) philosophies. Keywords : Oil Country Tubular Goods, Carbon Steels, High Strength, Sulfide Stress Cracking, Sour Environment, Hydrogen Sulfide, Heavy Wall, Casing, pH, C 110.