The paper presents a novel concept of a very efficient transportation engines for operation with CNG, LNG or LPG. The paper considers the options of single fuel design with jet ignition and dual fuel design with Diesel and gas. In the first option gas fuel is injected into the main chamber by a direct injector and ignited by jet ignition. In the second option gas fuel is injected into the main chamber by a direct injector and ignited by the direct injection of a small quantity of Diesel fuel. Injection and ignition may be tuned to control the amount of premixed and diffusion combustion to produce the best fuel conversion efficiency vs. load and speed requirements within the prescribed pressure and temperature constraints.