Abstract: A method of operating an internal combustion engine in which there is introduced into a combustion chamber, inert carrier gas, combustion supporting gas and fuel, the fuel is caused to combust in the combustion chamber and exhaust gas is exhausted from the combustion chamber wherein the carrier gas comprises a significant proportion of carbon dioxide and the exhaust gas is treated with water to remove from the exhaust gas and absorb in the water an amount of carbon dioxide generally equal to the quantity of carbon dioxide added by said combustion, and the thus treated exhaust gas is returned to the combustion chamber to provide the carrier gas. The carrier gas may have inert gas such as argon added thereto in proportions controlled such that the gamma value of the mixture of gases equals a predetermined value which may be approximately that of air.