This paper is the second in a sequence which develops a model of hot, high-pressure geothermal brines largely modelled on a common salt solution. The first paper described the T-p-X state-space. This paper proposes density correlations for a wide range of temperature T, pressure p and mass fraction of sodium chloride X. Using experimental and calculated data, formulae which closely approximate the density are given in terms of the primary variables T, p and X. These correlations cover the entire T-p-X state-space and can be used in subroutines suitable for use in numerical simulation programs.