Abstract: The present invention is a barrel-type internal combustion engine. The engine is generally comprised of a plurality of cylinders arranged in in-line pairs, each in-line pair having a double headed piston therein. The cylinders are arranged surrounding a central shaft that has a cam thereon. The cam has two opposing sinusoidal surfaces extending outward and around the shaft for positioning the pistons in the cylinders and transferring the combustion energy to the output shaft. The cam has a plurality of alternating and equidistantly spaced rises and reverse rises forming each of the sinusoidal surfaces. The engine is constructed and arranged to align each rise and reverse rise with a cylinder such that the engine can produce a power stroke substantially simultaneously in each cylinder aligned with a rise and reverse rise.