Isothermal P-x data and excess enthalpies have been measured at approximately 125 degrees C for the binary mixtures of octane + N-methylacetamide, cyclooctane + N-methylacetamide, and octane + acetic anhydride. For each binary system linear temperature dependent interaction parameters were fitted to experimental data using the NRTL model. Activity coefficients at infinite dilution were derived from the P-x data at low concentrations using a flexible Legendre polynomial.