Vapor-liquid equilibrium data for the mixtures propane + decahydronaphthalene (decalin) at (392, 439, and 415.5) K and propane + naphthalene at (373, 415, and 443) K are reported. The experiments have been conducted in a high-pressure cell at pressures up to 9 MPa. The molar concentrations have been measured by a spectroscopic method described earlier, which allows us to eliminate the effect of the baseline shifts. P-x coexistence curves are determined up to the mixtures critical points. The unusual shape of the bubble curve of the propane + naphthalene mixture at 373 K is probably due to the existence of a critical end point at a temperature close to this one.