Firmus Energy to raise gas prices by more than 12%
Firmus Energy is putting up gas prices by more than 12% from the end of March.
The company supplies about 50,000 customers in the greater Belfast area and a further 30,000 beyond Belfast.
The price increase means a typical household customer will see bills rise by £61 a year.
Last week, the other major gas supplier in Northern Ireland, SSE Airtricity, announced it was putting up prices by more than 7%.
Firmus Energy said the move reflects the "rising natural gas commodity market" - which has seen wholesale prices in the UK go up by more than 50% over the last 12 months.
Managing director Michael Scott said: "We understand the importance of price stability for customers and apologise for having to increase prices.
"Over the past three years we have been able to reduce or maintain our prices."
The price rise follows consultation with the Utility Regulator, the independent government department responsible for regulating the electricity, gas, water and sewerage industries in Northern Ireland.
It will come into effect for Belfast customers from 7 April and for non-Belfast customers from 31 March.
Kevin Shiels, from the Utility Regulator, told Good Morning Ulster that it was "satisfied" that Firmus were justified in raising gas prices.
"To put it into some context, this is the first rise in three years and actually in two of the last three years there have been price falls.
"It is unwelcome, of course, but it is reflective of underlying costs and we're satisfied that it is justified."
He added that overall gas prices are "below the levels seen in the Republic of Ireland and on a par with levels in Great Britain".
"So, gas customers in Northern Ireland can be satisfied that the regulator is protecting them and ensuring prices are being kept as low as possible."