Japan's SMBC Aviation Capital has bought 80 Boeing Co (BA.N) 737 Max planes, the largest order from an aircraft lessor for the upgraded variant of the narrow-body jet.

The deal is valued at more than $8.5 billion at list prices, although buyers typically get significant discounts.

This makes SMBC the 50th customer for the 737 Max since the plane was launched in August 2011. Boeing has secured more than 2,400 orders for it since then.

"This order is another example of our history of partnership with SMBC Aviation Capital and Japan," said Ray Conner, president and chief executive of BoeingCommercial Airplanes, in a statement.

"Today's announcement from a top leasing company is a vote of confidence in our 737 MAX and helps SMBC Aviation Capital capture the strong demand in the single-aisle market."

The 737 Max features a new engine developed by CFM, a joint venture between General Electric Co's (GE.N) aviation unit and French firm Snecma, as well as winglets and other improvements.

These help the aircraft to be 14 percent more fuel-efficient than the current models of the 737, said Boeing.

The U.S. planemaker has forecast that airlines will need more than 25,600 single-aisle planes like the 737 and Airbus Group NV's (AIR.PA) A320 over the next 20 years.

Narrow-body aircraft are used on routes of up to five hours, with fast-growing Asian low-cost airlines a major customer base for both leasing companies and manufacturers.

Lessors such as SMBC are an increasingly important source of these aircraft, given that they help airlines avoid the large initial capital investment that is needed when they order the planes directly from manufacturers.

"Today's announcement shows our ongoing commitment to the new generation of the popular 737 family, as well as our appetite to keep broadening and deepening our platform in order to service our customers' requirements," said SMBC CEO Peter Barrett in the statement.