Starting in the 1990s, the supply of electricity and gas to end consumers in the UK has been unbundled from the rest of the industry. At the time of privatisation, British Gas and one regional public electricity supplier (PES) held a monopoly on supplying all domestic gas and electricity consumers respectively in Great Britain. Between 1996 and 1999, domestic energy consumers were gradually able to choose their supplier, and finally in May 1998, the domestic gas market was fully opened to competition, closely followed by the domestic electricity market in May 1999.