A number of variations of the invention may include a fuel supply system for an internal combustion engine and/or method, wherein heat is exchanged from gaseous fuel in a gaseous fuel line and at least one of a liquid fuel in a liquid fuel feed line or a liquid fuel return line which are connected to an injection fuel rail of an internal combustion engine. In a number of variations, a regulator or throttling valve is provided in the gaseous fuel line to expand gas flowing therein and reduce the temperature of the gas to further cool the liquid fuel flowing in the liquid fuel feed line or the liquid fuel return line. Another variation may include a method comprising exchanging heat from gaseous fuel in a gaseous fuel line and a liquid fuel in a liquid fuel feed line or a liquid fuel return line which are connected to an injection fuel rail of an internal combustion engine. Another variation may further include throttling the flow through the gaseous fuel line to adiabatically expand the gas flowing and reduce the temperature of the gas to further cool the liquid fuel flowing in the liquid fuel feed line or the liquid fuel return line.