From the early beginning of what would become the DC-10 program, McDonnell Douglas wanted to offer an long-range aircraft side by side to the short-range, domestic model. These efforts led to the DC-10-20, whcih should become the second main version after the DC-10-10. The Series 20 was equipped with Pratt & Whitney's JT9D - engines, which offered the highest thrust available at that time. As these engines were also used on the early 747s, the Series 20 was targeted on 747 operators which needed a second long-range type in the fleet to fill the gap between the old DC-8s/707s and the new Boeing 747.

One of them was Northwest Orient Airlines, an airline with a large international network which became the launch costumer for the long-range model. Shortly afterwards, also the DC-10-30 was announced. The Series 30 was an aircraft with a similar range, but equipped with General Electric's new CF6-50 - engine which now competed with the JT9D. The airlines' interest switched from the Series 20 to the new model and so orders for the GE - powered aircraft came in. Nevetheless, Northwest Orient Airlines insisted to brand their aircraft as superior to the Series 30 which resulted in the new designation: DC-10-40.