New Gibbs ensemble Monte Carlo (GEMC) simulation results for vapor/liquid phase equilibria and new Monte Carlo simulation results for structure and thermodynamic properties of the hard core Yukawa fluids of variable range (HCYF-VR) are presented. Using the inverse temperature expansion of the free energy of mean spherical approximation a new version of the analytical theory of HCYF-VR has been developed. GEMC results for 108, 216, and 500 particles show a significant system size dependence of the vapor/liquid phase diagram. Comparisons of theoretical predictions with simulation data show that the analytical theory is highly reliable in describing structure, thermodynamic properties and phase equilibrium of HCYF-VR over a range of the attraction parameter and thermodynamic conditions. Both simulation and theoretical results show that the range of vapor/liquid equilibrium temperature shrinks as the range of interaction decreases. Theoretical results for the critical point and triple point temperatures illustrate that the vapor/liquid phase diagram tends to flatten out for sufficiently short range of the attraction, finally resulting in fluid/solid phase equilibrium, in agreement with simulation results. In addition, the analytical theory has been extended to predict thermodynamic properties of several binary HCYF-VR mixtures accurately.