US carrier Southwest Airlines has placed an order for 100 Boeing 737 MAX jets following a multi-year evaluation to modernise its fleet.

As part of the agreement, the carrier selected the 737-7 as its preferred replacement. The aircraft will join Southwest’s 737-8, which serves the 175-seat requirement.

With the latest deal, Southwest has a total of 200 737-7s and 180 737-8s in its order book.

The new order also includes an option to buy 155 aircraft across the two models under the agreement.

Southwest chairman and CEO Gary Kelly said: “Southwest Airlines has been operating the Boeing 737 series for nearly 50 years, and the aircraft has made significant contributions to our unparalleled success.

“Today’s commitment to the 737 MAX solidifies our continued appreciation for the aircraft and confirms our plans to offer the Boeing 737 series of aircraft to our employees and customers for years to come.”

Following the latest agreement, Boeing and its suppliers could build more than 600 new 737 MAX jets for the Southwest through 2031.

Both 737-7 and 737-8 MAX family aircraft are designed to consume less fuel and reduce carbon emissions by at least 14% compared with their replacements.

Boeing commercial airplanes president and CEO Stan Deal said: “Their fleet decision today brings more stability for our biggest commercial programme and will ensure that our entire 737 family will be building new airplanes for Southwest for years to come.”

Earlier this month, Canada’s WestJet reduced its order of 737 MAX aircraft by 15, leaving 27 737 MAXs on order.