The supply of gas to households in the greater Belfast area will be open to competition from next month.
Phoenix gas has completed the process to enable other suppliers to use its network - and four new companies could enter the market.
The four are Energia, Firmus, Scottish & Southern and Vayu.
All four of them have been involved in supplying businesses since 2006, but Phoenix has had the household market to itself for more than a decade.
When the business market was opened up, Phoenix saw 1,200 companies, representing 15% of its gas business, going to other suppliers.
However, Phoenix's operations director Ivan Bell said competition in the household market would be good news for consumers.
No changes will be needed to existing pipes or meters, but initially the utility regulator will only allow 300 people to switch supplier per week.
Up until now Northern Ireland has been a regulated market, with the utility regulator having the say on how much Phoenix Supply could charge.
It had to allow for the company to make a reasonable profit and to invest in the infrastructure.