The end of Phoenix Gas’ longstanding monopoly in the household gas market will come within weeks.
It is understood that rival supplier Firmus Gas will begin selling gas to homes in the greater Belfast area from next month.
The move – which is expected to encourage a price war – comes less than six weeks after Airtricity challenged NIE Energy’s domestic electricity monopoly.
Consumers can switch suppliers over the telephone and there is no need to have new equipment installed.
There is also a suggestion that Firmus will become the first dual supplier of both gas and electricity in Northern Ireland.
The opening of the domestic electricity market has seen up to 30,000 customers leave NIE Energy for Airtricity since June.