PARIS-- Airbus Group is close to bagging its biggest single order for commercial jetliners from India's IndiGo which is making a 250-aircraft, $25.7 billion bet on a boom in air travel in the world's second-most populated country.

IndiGo, a budget carrier which has become India's largest airline by number of passengers transported, has signed a memorandum of understanding for the order for A320neo planes, Airbus said on Wednesday.

At list prices, the order would be worth $25.7 billion, but plane manufacturers typically offer discounts to large customers for bulk orders.

The giant order by IndiGo bucks the recent trend among some Asian carriers to slow down the rate at which they have expanded to capture growth in the Asian air travel market as living standards rise across the region. Malaysia's AirAsia Bhd. and Singapore-based Tiger Airways Holdings have recently deferred or canceled orders.

Still, the Asia-Pacific region is expected to absorb much of the demand for new passenger jets. In Airbus's latest industry forecast, the largest number of planes, around 70% of the total to be built over the next 20 years will be single-aisle jets such as the Airbus A320 with demand in China and India for domestic flying helping drive 37% of these deliveries to Asia-Pacific airlines.

The Indian airline's order is the biggest Airbus has received since Indonesia" s Lion Group last year placed an order for 234 Airbus A320 planes, valued at a combined $22.4 billion at list price.

The A320neo, a new version of the Airbus's popular single-aisle A320 jets that includes a new engine and other devices to cut fuel consumption, made its maiden flight in late September.

Airbus has sold more than 3,250 of the planes, beating the more than 2,000 orders Boeing Co. has booked for its 737 Max, a similar upgrade the Chicago-based plane maker is undertaking for its best-selling single-aisle 737 jet.

The privately-held IndiGo is aggressively expanding to defend its position as rival low-cost Asian carriers are seeking to tap the rapidly growing Indian market.

IndiGo now has a fleet of 83 A320-200 single-aisle Airbus planes. The carrier had previously placed orders for 280 Airbus aircraft, a mix of different versions of the A320.

Privately held IndiGo, which is controlled by India's INterGlobe Enterprise Ltd., currently flies to 31 cities in India and five overseas, including Bangkok and Dubai.

Santanu Choudhury in New Delhi contributed to this article.

Write to Inti Landauro at inti.landauro@wsj.com

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