There are three main categories of heliports in Norway. Most land-based heliports are built in conjunction with or at hospitals. They are owned and operated by the respective hospital trust and are served by the Norwegian Air Ambulance. A second major group are offshore oil platforms and other installations related to the petroleum industry. These are owned and operated by the oil or gas field operator. The third-category are general-purpose heliports. These are often owned by helicopter operating companies.