Monte Carlo (MC) simulations have been carried out for mixtures of Lennard-Jones (LJ) fluids near or in the supercritical region. Excess molar enthalpy at equimolar concentration, H-p,x=0.5(E), has been obtained for four kinds of model mixtures each having different combining rule for unlike interactions. The pressure and temperature dependencies of H-p,x=0.5(E) are investigated. The unique pressure and temperature dependencies of H-p,x=0.5(E) for real systems such as (ethane + ethene) in the supercritical condition have been reproduced by the present simple model systems. Excess molar internal energies at constant volumes, U-V,x=0.5(E), are also evaluated. They are compared with H-p,x=0.5(E) to investigate the volumetric contributions to H-p,x=0.5(E) or excess molar internal energies at constant pressure, U-V,x=0.5(E). Calculated U-V,x=0.5(E) for the present model systems are quite simple compared to the excess molar internal energy at constant pressure, U-V,x=0.5(E). They are very small in magnitude and show linear dependencies on the density of mixtures.