Since Borneo is ruled by three countries - Malaysia, Indonesia & Brunei, it's better to sub-divide the island to understand the economy better.
Brunei, the abode of peace, is officially known as the Nation of Brunei. It is situated on the north coast of the island of Borneo and the only sovereign state enjoying the position of being the whole part of the island.
The state enjoys a wealthy economy. It is duly influenced by a combination of domestic and foreign entrepreneurship, government regulation, welfare measures, and village tradition.
Up to 90% of the state's GDP is dependent on crude oil and natural gas. Because of its rich oil resources, Brunei is the fourth-largest producer of oil in Southeast Asia.
Timber export was the primary resource of Sabah's economy, but with efforts to save forests and its flora and fauna, the palm oil trade has emerged as an alternative trade. Other agricultural products that Sabah trades in include rubber and cacao, along with fisheries and vegetables. With time, the tourism industry has turned out to be the second-largest contributor to the economy.
In the 70s, Sabah was one of the wealthiest states in the Malaysian Federation next to Selangor, but with time, today it is Malaysia's poorest state. It hasn't been able to make full use of its natural resources. It has one of the lowest average incomes and, ironically highest cost of living in Malaysia.
The situation is improving, with funds assigned to the state being increased and concentration diverted to developing rural areas, transportation, infrastructures, and sectors such as agriculture, manufacturing, and tourism, contributing to its economy.
Sarawak is one of the two Malaysian states situated in the northwest of Borneo. For decades, LNG and petroleum have been the primary sources of the Malaysian federal government's economy, while Sarawak merely receives a royalty of 5%. Tropical hardwood timber is the backbone of Malaysian exports, and Sarawak is one of the largest exporters of this wood.
The state's economy is also influenced by its rising tourism industry. Almost every year, the state witnesses a drastic increase in the number of tourists visiting Sarawak. Sarawak's main attractions include the Kuching city, the Gunung Mulu National Park, and the Rainforest World Music Festival.
Around 73% of the island of Borneo is covered by Kalimantan, the Indonesian territory, which is sub-divided into four major parts - East Kalimantan, West Kalimantan, North and South Kalimantan.
East Kalimantan's economy depends upon natural resources such as oil, natural gas, coal and gold mining. Balikpapan consists of a huge oil refinery restated by Indonesia Governance.
Other sources of income include agriculture and tourism. Major tourist attractions include Derawan Islands in Berau Regency, Kayan Mentarang National Park in Nunukan, Crocodile Husbandry in Balikpapan, deer husbandry in Penajam, Dayak's Pampang Village in Samarinda, and many more.
Many economic sectors support the economy of South Kalimantan. Agricultural sectors include rice, corn, peanuts, soybeans, coconut, rubber, cloves, and cacao. Livestock, fish products, and the forestry sector have a significant role in the economy of South Kalimantan.
The mining sector is ruled by petroleum, coal, diamond, gold, iron ore, and tiles. Wood carvings, rattan and wood furniture, reptile skins, and weaving are famous handicrafts.
Major exports for West Kalimantan are processed wood, rubber, and fish, while log, sawn timber, rattan, and resin come from Central Kalimantan.