New Zealand's per capita consumption of electricity is among the highest in the world. A network of transmission lines links all major power stations, bringing electricity to 99% of the population. Future hydroelectric potential is limited, however, and thermal power based primarily on coal and natural gas is becoming increasingly important. Total installed generating capacity was 8,512,000 kW in 2001. In 2000, net electricity generation was 37.8 billion kWh, of which 26.6 % came from fossil fuels, 66.4% from hydropower, and 7% from other renewable sources. Consumption of electricity in 2000 was 33.3 billion kWh. The geothermal power station at Wairakei has been operating since 1958, while a second at Ohaaki was commissioned in 1989.
In 1995, petroleum accounted for 43% of New Zealand's primary energy consumption; natural gas, 30%; coal, 17%; and hydroelectricity, 10%. The Kapuni natural gas field, discovered in 1959, began production in 1970; the Maui offshore natural gas and condensate field, one of the largest in the world, began production in 1979. Oil and gas exploration and development of indigenous resources continue to be stressed, in efforts to reduce dependence on imports. Crude oil and natural gas liquid production levels in 1998 were 47,000 barrels per day and 4.8 million cu m, respectively. Proven reserves of natural gas total 100 billion cu m (3.5 trillion cu ft); oil reserves, 200 million barrels. Coal mining began in the 1850s; over the last 40 years, coal's contribution to the energy supply has fallen from 50% to about 11%. In the 1990s, new coal mining activity was undertaken to meet increased demands for electricity and steel production. In 2002 coal production reached its highest level in New Zealand history (4 million tons). Coal reserves are estimated at 129 million tons, of which 85% is located in the untapped lignite fields in Southland.