The Electricity Corporation of New Zealand (ECNZ) was established in 1987 as a state owned enterprise to operate as a commercial, profit-making organisation. ECNZ was the sole provider of electricity in New Zealand, including generation, transmission and retail. Electricity was distributed through local electricity supply authorities.
In 1994, Transpower was separated from ECNZ and created as a state owned enterprise. Transpower own and maintain the national electricity grid, transmission lines and grid exit points for New Zealand.
In 1996, ECNZ was split into two more state owned enterprises, ECNZ and Contact Energy, and a wholesale electricity market was established. In 1999 Contact Energy was privatised.
The last significant reform was the separation of the lines and energy businesses of electricity supply companies. This resulted in the split of ECNZ into three competing state owned enterprises: Meridian Energy Limited, Genesis Power Limited and Mighty River Power Limited. The purpose of the reforms was to introduce a more dynamic and competitive environment into the generation, distribution and retailing of electricity.