SSE Airtricity is putting up gas prices by more than 7% from the end of this month.
The company supplies more than 140,000 customers in the greater Belfast area.
The price increase means a typical household customer will see gas costs rise by £36 a year.
The company said the price rise reflected "sustained increases in global wholesale gas costs which have risen by over 50% in the last 12 months".
The prices rise follows consultation with the utility regulator.
The regulator said: "We regulate the prices that SSE Airtricity Gas Supply can charge to its customers in the Greater Belfast area and have carefully reviewed each element of this new tariff.
"This increase will still leave the SSE Airtricity Gas Supply domestic tariff for Greater Belfast lower than the average standard tariff in the Republic of Ireland and amongst the lowest standard gas tariffs in the UK. "