EasyJet has claimed air fares on some routes could be cut by almost a third if a new runway is built at Heathrow Airport.
Passengers could benefit from cheaper deals as a result of "increased competition" from budget airlines, it said.
The Luton-based company has urged MPs to support plans for a third runway.
It said fares at the low-cost airline are about 30% lower than those on legacy carriers.
EasyJet said the proposed expansion paves the way for budget carriers to use the airport "at scale" for the first time.
The company already operates from other major "hub" airports such as Amsterdam Schiphol and Paris Charles De Gaulle.
EasyJet said it has been working closely with Heathrow for several years to ensure its requirements will be met if the new runway is approved.
Chief commercial officer Robert Carey said: "This expansion would enable low cost airlines to provide new routes and increased competition on dozens more UK and European routes.
"EasyJet's costs are significantly lower than legacy airlines so EasyJet's fares on these services would be lower than those paid by passengers today."
Heathrow's plan to build a third runway was given the support of the cabinet last week and MPs will soon vote on it.
Transport Secretary Chris Grayling said the £14bn runway, which could be completed by 2026, would be funded entirely privately.
Opponents argue that a new runway will breach the UK's legal limits on air pollution and increase noise pollution, with an extra 700 planes a day.
But EasyJet said it was committed to sustainability and its A320neo aircraft are quieter and use less fuel than older models.