Borneo has a tropical climate, with an average annual temperature
of 260c (78f). Extreme humidity prevails in many parts of the island, especially in the coastal regions. Rainfall is heavy, averaging around 4064 mm (160inches) annually for the island as a whole and considerably more in some localities. Maximum rainfall occurs between October and May, the period of the north eastern monsoon. There is no dry season.

Vegetation is abundant and highly diversified. In the mountainous regions rhododendron, orchid, pitcher plants, and other flowering plants grow in great profusion. Indigenous fruit trees include the coconut palm, orange, banana, and mango. More than 50 species
of timber trees grow in the dense forests, notably teak, ironwood, ebony, and sandalwood.

Elephants and rhinoceroses live in the northern portion of the island, as do the orangutan, gibbon, proboscis monkey, and wild ox. Among the smaller quadrupeds are several species of macaque monkey, tiger cat, tapir, honey bear, porcupine, flying squirrel, flying fox,
and various species of deer. Reptiles include the crocodile, many varieties of lizard, and the python and numerous other species of snakes. Eagles, falcons, vultures, parrots, peacocks, flamingoes,
and hornbills are among the birds found here.

The main mineral resource of the island is petroleum, found primarily in Brunei and along the east coast near Balikpapan. Other minerals include coal, gold, copper, tin, iron, manganese, antimony, bauxite, gypsum, marble, rock salt, mercury, diamonds, and sulfur. Agricultural products include rice, millet, maize, manioc, sweet potatoes, yams, sugarcane, cucumbers, pumpkin, and tropical fruits. Such products as rubber, coconuts, tobacco, manila hemp, pepper, coffee, cinnamon, and camphor are cultivated for export.