Bombardier Aerospace says an unidentified buyer has placed a conditional order for five CS100 and 10 CS300 jetliners.
Bombardier says based on list prices for the aircraft, the contract is valued at about US$1.02 billion.
The company says the customer is new and wants to be unidentified.
CSeries aircraft will enter into service late next year.
With this conditional order, Bombardier has 12 customers for the planes, and nine firm orders.
The CSeries aircraft are designed for the 100- to 149-seat market.