Accurate knowledge of hydrogen gas viscosity is extremely important for developing a hydrogen economy. There is a need for recommendations relating to the best available viscosity data and the best available correlations for practical purposes. The purpose of this work is to analyze the various possibilities for viscosity correlation to estimate hydrogen gas viscosity in the high pressure and high temperature region for practical industrial uses. We recommend suitable force constants and a collision integral for the Chapman-Enskog solution to estimate viscosity in the limit of zero density. At high density, modification of Diller's extrapolation equation for excess viscosity gives good agreement with the available experimental data. A combination of the Chapman-Enskog solution and modification of Diller's excess viscosity gives an estimation of hydrogen gas viscosity within 2 to 4 % deviation from the existing experimental data for the high-temperature and high-pressure region.