Abstract: An oil pan for an internal combustion engine is an assembly of a tank member defining a deep interior space section for storing a lubricating oil, and a main frame member having a shallow bottom defining a shallow interior space section for collecting the oil. The main frame member further includes first and second side walls defining a bottomless open interior space section for leading the oil from the shallow interior space section into the deep space section. The main member is further formed with at least one transverse bridge extending over the bottomless open space section between the side walls to improve the rigidity. The transverse bridge is reinforced by a longitudinally extending projection such as a thin wall rib projecting laterally from one of the side walls or a flow regulating barrier projecting upward from the shallow bottom.