Throughout the world, research and development in the field of vehicle transportation is increasingly focusing on engine and fuel combinations. The conventional and alternative fuels of the future are seen as fundamental to the development of a new generation of internal combustion engines that attain low well-to-wheel CO2 emissions along with near-zero pollutant emissions. With its recognized expertise in both fuels and engines, IFP is in an ideal position to host an international event focusing on these issues and, as such, decided to organize an international conference entitled "Which Fuels for Low CO2 Engines?". Following the success of the previous IFP conference in 2001 on the theme of "New HCCI Combustion Processes", this new event provided once again an opportunity for experts from the automotive industry, the heavy-duty and small engine sectors, fuel companies, additive makers, OEM suppliers and R&D organizations to discuss the potential of this new generation of fuels and energy conversion in engines. The content of these proceedings is organized around the five following technical sessions: Future of liquid fuels, Engine and fuel-related issues in HCCI & CAI combustion, Energy conversion in engines from natural gas, Use of hydrogen in IC engines, Which fuels for low CO2 engines? This international conference attracted specialists in the field, including participants from universities, research centres and industry.