Isobaric heat capacities for the n-pentane-acetone and the methanol-acetone binary mixtures were measured with a flow calorimeter at selected temperatures from 423.1 K to 523.1 K as a function of pressure up to 10 MPa. The compositions of each mixture were 0.25, 0.50, and 0.75 mole fractions. The uncertainties of c(p) measurements were less than 0.4%, depending on the magnitude of the temperature differences. As part of the measurement process, liquid densities at elevated pressure and 303.1 K were also determined and reported. Experimental c(p) data were compared to the c(p) values calculated using several equations of state. In general none of the equations of state were able to reliably predict the heat capacities in the supercritical region for either mixture. For both mixtures, the use of binary interaction parameters improved the c(p) representation in the critical region, by effectively translating the pressures that correspond to cp maxima. However, very close to a maxima, deviations of the calculated c(p) were still as large as 50%, due to the deficiencies of cubic equations of state in the critical region. Comparison results are specifically presented for the Peng-Robinson equation of state