This International Standard provides guidelines and requirements for material selection of both seamless casing and tubing, and downhole equipment for CO2 gas injection and gas production wells with high pressure and high CO2 content environments [higher than 10 % (molar) of CO2 and 1 MPa CO2 partial pressure]. Oil production wells are not covered in this International Standard. This International Standard only considers materials compatibility with the environment.Guidance is given for the following:— corrosion evaluation;— materials selection;— corrosion control.This International Standard is aimed at high CO2 content wells, where the threat of low pH and CO2 corrosion is greatest. However, many aspects are equally applicable to environments containing lower CO2 concentrations.Materials selection is influenced by many factors and synergies and should be performed by either materials or corrosion engineer.