The basin covers a surface of about 170,000 to 200,000 square kilometres (66,000 to 77,000 sq mi) and has a NNW-SSE oriented shape.

[1][2] The basin is bounded to the west by the Andes mountains and is separated from the Malvinas Basin to the east by the Río Chico-Dungeness High.

[3] Rocks within the basin are Jurassic in age and include the Cerro Toro Formation.

[4] Three ages of the SALMA classification are defined in the basin; the Early Miocene Santacrucian from the Santa Cruz Formation and Friasian from the Río Frías Formation and the Pleistocene Ensenadan from the La Ensenada Formation.

The Magallanes Basin contains most of Chile's coal reserves dwarfing those found in the Arauco Basin or around Valdivia (e.g. Catamutún, Mulpún).