Recently a new experimental technique of vanishing interfacial tension (VIT) has been developed to enable rapid and cost-effective determination of miscibility in gas-oil systems. In this study, VIT experiments have been extended to two standard gas-oil systems of n-decane-CO2 and live decane-CO2 at elevated pressures and temperatures. The VIT miscibilities of the two standard gas-oil systems and the two reservoir crude oil-gas systems, namely Rainbow Keg River (RKR) and Terra Nova, were compared with Peng-Robinson (P-R) equation of state (EOS) calculations. The close match of VIT miscibilities with other conventional experimental techniques in the standard gas-oil systems, as well as the reasonable match obtained with untuned PR-EOS calculations for several systems studied, clearly demonstrates the sound conceptual basis of VIT technique to determine fluid-fluid miscibility in multi-component hydrocarbon systems.