Energia has signed a deal to supply gas to the Dublin Airport Authority (DAA) that is worth €4.2 million annually.
Under the terms of the contract, Energia, the electricity supply arm of Viridian, will supply gas to three of the DAA's sites in Dublin and Shannon.
In addition to supplying gas to the authority, Energia also supplies electricity to 41 DAA sites from Viridian's gas-fired power station in north Dublin.
Energia - which supplies gas and electricity to the business sector - is a recent entrant into the gas market. It has a 25 per cent market share of the all-island business electricity market and is ESB's main rival.