Oceanus Procellarum is a vast lunar mare on the western edge of the near side of the Moon. It is the only one of the lunar maria to be called an "Oceanus", due to its size: Oceanus Procellarum is the largest of the maria, stretching more than 2,500 km across its north–south axis and covering roughly 4,000,000 km², accounting for 10.5% of the total lunar surface area.
