Abstract: An internal combustion engine and a method of controlling an internal combustion engine are provided, that are more efficient than existing engines. The internal combustion engine includes a combustion chamber, and the engine is configurable to operate in: a compressionless operating mode where the engine is driven by combustion of fuel and oxidant in the combustion chamber without compression of the fuel and oxidant; and a compression generating operating mode where the engine is used to compress fluid in the combustion chamber.