ESDU 95020 tabulates the viscosity of twenty carboxylic (alkanoic) acids at saturation pressure, for temperatures from just above the melting point to approximately 0.9 of the critical temperature. Experimental data extracted from the literature were fitted by an equation for the logarithm of dynamic viscosity as a function of reduced temperature. The equation contains four constants and the values determined for them are tabulated for each compound. The constants were chosen in such a way that within each compound group (homologous series), their values varied progressively throughout the series and, simultaneously, provided acceptable fits to any reliable data. Viscosities are tabulated at 10 K and 10 degree Celsius intervals, together with an assessment of the uncertainty in each value. The sources of the data for each compound are listed, and the critical temperature is given. It is noted that viscosity increases by 1 per cent for a pressure increase of 1 MPa and an equation is suggested for calculating the effect of pressure up to 50 MPa. A full bibliography is given of the sources consulted.