There is current interest in evaluating the greenhouse gas emissions and net energy production associated with oil recovery processes. In this study, methods have been formulated to calculate balances of energy and environmental load (greenhouse-gas emissions) of gas injection projects. The environmental load per unit net energy produced is also calculated. The energy balance is the ratio of the energy consumed to the energy in the oil and gas produced. The environmental load balance concerns the ultimate greenhouse-gas equivalent CO2 emissions to the atmosphere resulting from the process. It is the ratio of the potential emissions saved through retention of injected gas in the reservoir to the emissions arising from combustion of the produced oil and gas and from facility operation. Example calculations for several gas injection projects have shown that : (i) The energy requirements of the facilities are generally less than about 15% of the produced energy. (ii) Both energy and environmental load balances tend to be higher for tertiary projects than comparable secondary projects due to the lower gas utilization in the former. (iii) The energy balance is highest for hydrocarbon gas projects and the environmental load balance is also appreciable. (iv) In terms of net environmental load per unit energy produced, CO2 projects are more favourable than hydrocarbon and nitrogen projects, by up to about 50% in some cases. The load per unit energy for hydrocarbon and nitrogen projects is generally about 5-15% higher than that which would arise if facility operation and gas retention are neglected.