Brazilian budget carrier Gol is to buy 60 new-generation Boeing 737 Max aircraft in a deal worth $6 billion.
It is the largest order placed with the US aircraft manufacturer by a South American carrier.
The aircraft are due to be delivered from 2018.
Gol chief executive Paulo Kakinoff said: “The decision to order Boeing 737 Max is in line with our commitment to maintaining a modern and safe fleet that will allow us to sustain our competitive advantage in the long term.
“The new airplanes will have one of the best cost-benefit ratios in the market due to its unique operational economy, so it is fully compatible with our low-cost model.”
Gol said the new aircraft were 13% more fuel-efficient than its current fleet and would help to cut costs.