A highly-efficient, yet simply constructed internal combustion engine includes an intake cylinder to accommodate intake and pre-compression of an oxidizing agent, a combustion cylinder to accommodate a further compression of the oxidizing agent, an injection and ignition of fuel, and a partial expansion of combustion gases produced by the ignition of fuel; and an exhaust cylinder to accommodate a further expansion of the combustion gases and subsequent exhausting of the further expanded combustion gases. A reciprocating piston is inside each of the intake, combustion and exhaust cylinders and a crankshaft is coupled to the reciprocating pistons. A first transfer passage facilitates flow of the pre-compressed oxidizing agent from the intake cylinder to the combustion cylinder and a second transfer passage facilitates flow of the partially-expanded combustion gases from the combustion cylinder to the exhaust cylinder.