The purchase agreement follows a tentative deal for four 272-seat twinjets reached towards the end of last year.
Aerolineas has yet to disclose an engine selection for the aircraft.
It had originally said it intended to take delivery of two in early 2015, and complete deliveries in 2016, but Airbus has not given a delivery schedule.
The airline will operate the type on medium- and long-haul routes from Buenos Aires to destinations in Latin America, Europe and the USA.
“We are very proud of this decision, which makes our relationship with Airbus stronger than ever,” says Aerolines president Mariano Recalde.
Aerolineas is already an A330 operator, with four of the type, and the carrier’s fleet also includes a dozen A340s