SMBC Aviation Capital ordered 100 Boeing 737 MAX aircraft on Monday, placing the largest-ever purchase of the 737-10 by an aircraft lessor and expanding one of the industry's biggest narrowbody portfolios.

The agreement includes 60 737-10s and 40 737-8s. It also marks SMBC Aviation Capital's first order for the largest member of the 737 MAX family.

With the latest purchase, the lessor's portfolio of owned, managed and committed 737 MAX aircraft grows to 450 jets.

The order provides another boost for the 737-10, which is still awaiting certification by the U.S. Federal Aviation Administration. Boeing expects the aircraft to receive approval before the end of the year, allowing deliveries to begin shortly afterward.

The 737-10 seats up to 230 passengers and competes directly with the Airbus A321neo, the largest-selling aircraft in the single-aisle market. Its higher capacity allows airlines to carry more passengers on busy routes while reducing operating costs per seat

Aircraft lessors have become increasingly important customers for Boeing and Airbus, purchasing aircraft years before airline demand materializes and placing them with multiple operators through lease agreements.

Boeing said leasing companies now account for more than 1,450 orders for the 737 MAX family, or about one-fifth of the program's backlog.