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Orcus Patera is a region on the surface of the planet Mars first imaged by Mariner 4. It is a depression about 380 km long, 140 km wide, and about 0.5 km (500 meters) deep but with a relatively smooth floor. It has a rim up to 1.8 km high. Orcus Patera is west of Mons Olympus and east of Elysium Mons. It is about halfway between those two volcanoes, and east and north of Gale crater.
It has experienced aeolian processes, and has some small craters and graben structures. However, it is not known how the patera originally formed. Theories include volcanic, tectonic, or cratering events. A study in 2000 that incorporated new results from Mars Global Surveryor along with older Viking data, did not come out clearly in favor of either volcanic or cratering processes.
Mars Express observed this region in 2005, yielding a digital terrain model and color pictures.