A new set of constants for the modified Benedict-Webb-Rubin (MBWR) equation based on the Lennard-Jones (LJ) potential were obtained in the temperature range T* = 0.45 to T* = 6.0 by supplementing computer simulation data with data obtained by recalculating the first five virial coefficients of the LJ potential. These virial coefficients are presented in a detailed table that is suitable for the calculation of the internal energy and pressure of the LJ fluid in the vapor state. The MBWR equation was also extended to the alkanes by including a temperature-dependent energy parameter in the LJ potential. The resulting equation was found to be satisfactory for correlating experimental data for the liquid density and vapor pressure and in predicting the heat capacity of n-alkanes upto n-hexadecane. Only three parameters are required to characterize each iz-alkane, and furthermore, the parameters show regular behavior with the number of carbon atoms in the n-alkane.