Commodore Reef, also known as Rizal Reef, is a atoll located in the southeast of Dangerous Ground in the Spratly Islands in the South China Sea. It is located east of the Ardasier Reef and Investigator Shoal, 117.9 miles (189.7 km) NE of Swallow Reef and 167.1 miles (268.9 km) SE of Cuarteron Reef. The rock has been legally declared a rock.

The South China Sea is a marginal sea of the Western Pacific Ocean. It is bounded in the north by South China, in the west by the Indochinese Peninsula, in the east by the islands of Taiwan and northwestern Philippines, and in the south by the Indonesian islands of Borneo, eastern Sumatra and the Bangka Belitung Islands, encompassing an area of around 3,500,000 km2 (1,400,000 sq mi). It communicates with the East China Sea via the Taiwan Strait, the Philippine Sea via the Luzon Strait, the Sulu Sea via the straits around Palawan, and the Java Sea via the Karimata and Bangka Straits. The Gulf of Thailand and the Gulf of Tonkin are part of the South China Sea.