The methods of operation of four of the leading combustion system designs for fuel only gasoline direct injection (G-DI) engines have been compared by applying a classical analysis procedure for defining fuel transport. The fuel spray requirements for the different systems are discussed in relation to results obtained from a Phase Doppler Anemometry (PDA) rig for different injectors. The combustion systems have then been considered regarding the functional requirements of future G-DI engines. These include power potential, stratified and homogeneous performance, variable air motion requirements, OEID component function monitoring, packaging and manufacturing issues and calibration effort. The paper concludes that there are at least four main approaches capable of producing acceptable combustion and that the choice of system will depend on packaging, cost and manufacturing constraints.