ESB: By far the largest company in the sector with 19 generating stations. It is likely to remain the main supplier in the domestic sector for many years. Its tariffs are regulated by the Commission for Energy Regulation.

Bord Gáis: Holds 18 per cent market share among industrial and commercial users. It does not own any power stations and gets it power from an auction process and from the Synergen plant in Ringsend, Dublin.

Airtricity: A wind energy company headed by Eddie O'Connor, former boss of Bord na Móna. It offers a domestic product.

RWE: One of the largest energy companies in Europe. It significantly increased its Irish presence last year by concluding a €750 million deal with the Tynagh Energy power station in Galway. The German company has said it might enter the domestic market at some point.

Energia: This is the retail arm of the Northern Ireland electricity company, Viridian. It is already a major competitor for the ESB in the industrial and commercial market. It has not shown any sign of entering the domestic market.

CHP:(Combined Heat and Power) There are several small and medium-sized companies offering this service, instead of conventional electricity. The industry claims to have several thousand customers.

Direct Energy: A small company set up by some former telecoms executives. It is licensed to supply electricity by the CER, but has yet to enter the market.