In gas wells, where a low or unknown amount of the naturally occurring saline formation water is expected to be produced, tubing material selection relies on selecting a fixed dataset of input parameters and extrapolating to the entire well life. This is intended to represent the worst-case scenario; while this can be the case regarding pressure and temperature, the produced water composition as a function of time is less likely to be as reliable. This is because during production, gas can cause water evaporation, leading to a significant increase in the chloride ion concentration compared to the analyzed values – and hence, potentially an unsuitable material selected. To this end, it is important to: (a) ensure that the formation water composition analyzed is correct, (b) that this composition is reconciled to initial reservoir conditions and (c) calculate any evaporation/condensation effects in different sections of the well as a function of production forecasts. This makes it easier to establish operational envelopes that both prevent productivity impairment and provide appropriate thresholds of acceptability for the tubing material selected. This paper describes the methodology applied for tubing material selection for a high temperature-high pressure (HTHP) gas well in the North Sea.