Real Gas Properties. A Fortran subroutine called GASP (for Gas Properties) calculates the thermodynamic and transport properties for ten pure fluids: parahydrogen, helium, neon, methane, nitrogen, carbon monoxide,oxygen, fluorine, argon, and carbon dioxide. The pressure range is generally from 0.1 to 400 atmospheres (to 100 atm for helium and 1000 atm for hydrogen). The temperature ranges are from the triple point to 300 K for neon; to 500 K for carbon monoxide, oxygen and fluorine; to 600 K for methane and nitrogen; to 1000 K for argon and carbon dioxide; to 2000 K for hydrogen; and from 6 to 500 K for helium. GASP accepts any two of pressure, temperature, and density as input conditions. In addition, pressure and either entropy or enthalpy are also accepted as input variables, a desirable flexibility for cycle analysis. The properties available in any combination as output include temperature, density, pressure, entropy, enthalpy, specific heats, sonic velocity, viscosity, thermal conductivity, and surface tension. Also, the partial derivatives of pressure with respect to density at constant temperature as well as the partial derivative of pressure with respect to temperature at constant density will be computed. The subprogram design is modular so that the user can choose only those subroutines necessary to the calculations. Gasp was written for the engineer who requires both accuracy and speed in calculating thermodynamic and transport properties.