Airbus SE is close to winning an order for 300 jets from Indian budget carrier IndiGo, in what would be one of the European planemaker’s biggest-ever deals, according to people familiar with the matter.

The purchase would involve single-aisle planes in the A320 family, including the latest XLR variant, according to the people, who asked not to be named discussing a private matter.

A order, valued at more than $30 billion based on sticker prices, would represent the latest victory for Airbus as rival Boeing Co. reels from the grounding of its best-selling 737 Max. For IndiGo, which has already ordered more than 500 Airbus jets, the purchase would help widen its lead in the world’s fastest-growing major aviation market.

IndiGo is embarking on an ambitious expansion plan, especially in international markets, seeking to eventually connect cities such as London with India. Founded in 2005 by ex-US Airways Chief Executive Officer Rakesh Gangwal and former travel agent Rahul Bhatia, it has quickly outpaced all its rivals to grab almost half of the local market, making both founders billionaires.

In an interview earlier this year, CEO Ronojoy Dutta flagged that the airline was preparing to make another large order. Its smallest order so far was for 100 A320 jets in 2005 worth $6 billion at list prices at the time.

The Indian aviation market has lured the likes of Singapore Airlines Ltd. and AirAsia Bhd. to set up local units. But provincial taxes make India one of the most expensive places on Earth to buy jet fuel and intense competition there has often driven fares below cost, making profits elusive for most airlines.

The A320 family is a class of single-aisle planes that outsell all other types of aircraft from Airbus. The A320neo — of which IndiGo is the top customer — is the best seller within that line of jets and was priced at $110.6 million each in 2018, although discounts are common.

Representatives at Indigo, which is operated by InterGlobe Aviation Ltd., didn’t immediately respond to requests for comment. Airbus declined to comment. Reuters earlier reported on the order.