United Airlines has agreed to purchase a batch of used Boeing 737-700s, and intends to start taking delivery of the jets before the end of this year.
The airline is to take 19 of the twinjets and expects deliveries to begin in December.
United Airlines has not elaborated on the decision, which it disclosed in a brief note within its second-quarter financial results. Nor has it given a source for the jets.
The US operator has 40 of the type in its fleet, according to Cirium's Fleets Analyzer.
United is a user of the Boeing 737 Max with 14 of the Max 9 variant.
The airline's official fleet plan indicates that this will rise to 30 Max jets by the end of this year, with another 28 due in 2020, but United points out that this does not take into account delays from the suspension of deliveries following the Max grounding.
United generated second-quarter net income of $1.1 billion, with pre-tax earnings of $1.4 billion, as passenger revenues rose 6.1% over the three-month period.
It says it achieved the highest second-quarter pre-tax income in its history, attributing this to the "continued successful implementation" of its business strategy.
Chief executive Oscar Munoz says the airline is "now consistently delivering results for our customers as well as investors" and that it is raising its full-year earnings-per-share guidance to $10.50-12.
"Top-tier results are now the expectation, not the exception for United," he adds.