A dual-chamber oil pan includes an oil pan provided below an engine block, an oil pan separator that is provided within the oil pan and defines a first chamber communicating with the engine block, and a second chamber provided around the first chamber, and a suction port disposed within the first chamber. The first chamber includes a large-capacity portion including a bottom portion of the oil pan separator, and a small-capacity portion located above and integrally formed with the large-capacity portion.