Amazon has announced the purchase of 11 Boeing 767-300 aircraft including four secured from Calgary-based WestJet.

According to the online retailer, the aircraft were purchased from WestJet in March 2020 and will join the Amazon Air fleet this year after the completion of passenger to cargo conversion. Details of the sale agreement have not been released.

Amazon says the other seven planes were purchased from Delta Air Lines.

"Our goal is to continue delivering for customers across the U.S. in the way that they expect from Amazon, and purchasing our own aircraft is a natural next step toward that goal," said Sarah Rhoads, vice-president of Amazon Global Air, in a statement released Tuesday. "Having a mix of both leased and owned aircraft in our growing fleet allows us to better manage our operations, which in turn helps us to keep pace in meeting our customer promises."