ESDU 91040 provides evaluated thermophysical properties data for carbon monoxide. Equations@ based on a critical evaluation of experimental data in the literature are given for the variation with temperature along the saturation line for the following liquid and vapour properties: density@ specific enthalpy@ specific heat capacity at constant pressure@ dynamic viscosity and thermal conductivity. Also given are equations for the variation with temperature along the saturation line of the vapour pressure@ latent heat of vaporisation and surface tension. Also presented are equations for the variation with temperature of the specific heat capacity at constant pressure and specific enthalpy in the ideal gas@ the dilute gas dynamic viscosity and the dilute gas thermal conductivity. Saturation line properties in SI units@ calculated from the equations are tabulated at 2 K intervals and at 2 degree Celsius intervals from the triple point temperature to the critical temperature for the vapour pressure@ saturation densities@ enthalpies and surface tension and to within at least 10 kelvin of the critical temperature for the remainder. Ideal and dilute gas properties@ also in SI units calculated from the equations are tabulated at 20 K and at 20 degree Celsius intervals from the triple point temperature to 1000 K. In the absence of experimental data@ the tabulated data are extrapolated values and these are indicated in the tables. Conversion factors to facilitate use of the equations and tables in British units are included. A full bibliography is given of the sources consulted.