According to actual ecological tendency in recent years, in order to reduce greenhouse effect, more often the possibility of carbon dioxide deposition in geological structures is considered. There is some experience in this scope in Poland, relevant to injection of acid gas from sour gas sweetening facilities into oil or gas reservoirs. Developed technology is a result of research project performed in Polish Oil and Gas Institute with cooperation with Polish Oil and Gas Company and AGH University of Science and Technology. In 1993 and 1996 two industrial plants for acid gas injection have been activated. Acid gas reinjection eliminates sulfur compounds and carbon dioxide emission into atmosphere. The main task is to reduce environmental impact of the gas sweetening process, however injected sour gases increase also efficiency of reservoir production, displacing light hydrocarbons from underlying reservoir waters. The authors were involved in designing and monitoring of the injection systems for more then 10 years. This experience allows us to evaluate the process in respect of technology and ecology and to perform the analysis of injection impact on the reservoir performance. This paper discusses some technological considerations for acid gas injection and some physical phenomena influencing process efficiency. Also computer simulation results in comparison with current field observations are reported. The first sour gas injection facility reported here, injects gas containing about 15% H2S and 4 % CO2 into oil reservoir, at average rate of 250 000 Nm3/month. Laboratory tests performed on slim tube models have showed that at the actual reservoir pressure, the oil displacement process will be immiscible, achieving theoretically final recovery of 60%. Presently recovery factor is above 40%. The second plant reinjects acid waste gases from the process of amine sweetening of natural gas into the reservoir zone. Similar technologies, where acid gases from sweetening process are injected into gas/oil reservoirs are known in the literature however the acid gas is usually disposed into water saturated layers that have no contact with the gas reservoir. Project implemented in Poland had shown that it is possible to inject acid gas directly into water layer having hydrodynamic contact with gas reservoir without negative impact on produce natural gas composition. Previous computer simulations and PVT tests had showed that there would be no H2S inflow into the gas cap for more than 12 years, and this was confirmed by the current reservoir performance.