Abstract: Various embodiments are disclosed to utilize various fuels, including liquid natural gas fuels, to improve engine efficiency in gas turbine engines. In one configuration, a fuel is heated by a heat exchanger utilizing waste exhaust heat of a gas turbine engine. In another configuration, LNG fuel is heated using a pre-cooler for the inlet air stream of a gas turbine engine. In another configuration, fuel is injected into the pressurized air, downstream of the air-to-air intercooler. In yet another configuration, fuel is pumped through the engine's intercooler or a secondary heat exchanger exchanging heat with the compressed air stream between the low-pressure compressor and high-pressure compressor. In another configuration, the fuel is first heated by the intercooler and then further heated by a heat exchanger utilizing waste exhaust heat of the gas turbine engine.