The engine is called OPOC, short for opposed-piston, opposed cylinder. Inside each of the OPOC's two cylinders, two pistons slide in opposite directions. EcoMotors says this design, which uses half the parts of a normal internal combustion engine, allows the OPOC engine to achieve up to 20 percent greater mileage than the current most advanced gas or diesel engines. In its key operating range, a diesel OPOC could convert as much as 48 percent of its fuel's energy into work, beating today's best diesels. Moreover, an OPOC engine is just half the size and weight of a comparably powered conventional engine, which reduces the burden of moving its own mass.