Abstract: A hybrid internal combustion engine having a cylinder, a piston disposed within the cylinder, said piston constructed and arranged to reciprocate within said cylinder, and a combustion chamber defined by the cylinder and the top of the piston. The hybrid internal combustion engine also includes an exhaust manifold and a heat exchanger is disposed within the exhaust manifold. A pump disposed between the heat exchanger and a fluid reservoir is provided to deliver fluid to from the reservoir to heat exchanger, whereby the fluid in the heat exchanger is heated and turned into high pressure gas (HPG) when the combustion gases are exhausted from the combustion chamber via the exhaust manifold. The resulting HPG may then be introduced into the combustion chamber to provide a HPG power stroke.