In this study, a survey of research papers on the effect of carbon dioxide/natural gas mixture on the performance characteristics of an Internal Combustion Engine (ICE) is carried out. Generally, the presence of high carbon dioxide content in natural gas reduces the heating value of the mixture when compared with pure natural gas. This leads to reduction in the burning velocity which ultimately affects the engine output and thermal efficiency. However, there is an improvement in the NOx emissions while unburnt hydrocarbon and carbon monoxide are on the increase. Different techniques to improve engine performance were suggested and carried out. In addition to this, a direct injection fuel delivery system together with maintaining the air flow ratio is proposed as a way engine performance may be improved and emissions are reduced. © 2012 Asian Network for Scientific Information.