Located 143 kilometres (89 mi) northwest of Pitcairn Island, at 23°55′26″S 130°44′03″W / 23.92389°S 130.73417°W / -23.92389; -130.73417. Oeno Atoll measures about 5 kilometres (3.1 mi) in diameter, including the central lagoon, with a total area exceeding 20 square kilometres (7.7 sq mi). There are two larger and three smaller islets on or within the rim of the atoll. Their aggregate land area is only 0.69 square kilometres (170 acres). Oeno Island serves as a private holiday site for the few residents of Pitcairn Island, who travel there and stay for two weeks in January.
The main island (Oeno), about 0.5 square kilometres (120 acres) in area, has forest and scrub with pandanus and palm trees. It is located in the southwest part of the atoll's lagoon. There is a water tap installed on the island. The maximum elevation is less than 5 metres (16 ft). Sandy Island (or Islands) is to the northeast and may be an ephemeral island. Three smaller islets are to the south and west of the main island.
Oeno is the only land from which the total Solar eclipse of July 2, 2019 will be visible outside South America.
The island has been identified by BirdLife International as an Important Bird Area (IBA) principally for its colony of Murphy's petrels, which, at some 12,500 pairs, is estimated to be the second largest colony of these birds in the world.