Abstract: An internal combustion hydraulic engine for producing a supply of pressurized hydraulic fluid includes a frame, a pair of pivot pins, two levers, and combustion assemblies and hydraulic assemblies mechanically communicating with each other through the levers. Each of the assemblies includes a pair of opposed pistons engaged to the levers with a variable volume chamber between them, the piston faces being movable boundaries defining the variable volume chamber. In cyclic operation, a compressed fuel-air mixture in a first combustion chamber detonates, driving the combustion pistons apart. The pistons drive connecting rods, pivoting the lever arms, the lever arms, in turn drawing apart the pistons of a first hydraulic assembly, driving together the pistons of a second hydraulic assembly to produce pressurized hydraulic fluid, and driving together the combustion pistons of a second combustion assembly into which a fuel-air mixture has been introduced, compressing the mixture therein.