LONDON — Boeing announced on Sunday that it would be expanding the capacity of its 737 MAX 8 to 200 seats, up from the previous 189. The change would leapfrog its nearest competitor, the Airbus A320neo, by eleven seats and open up a fresh capacity gap between the two.

The addition will be accomplished, says Boeing, by adding an additional set of exit doors in the rear third of the aircraft. Furthermore, seat pitch will be reduced to 29 inches per seat. The company says the change will increase fuel efficiency per seat-mile by twenty percent over today’s 737 Next Generation 800. Boeing declined to provide further comment.

The move effectively leapfrogs the capacity increase of the 737’s nearest competitor, the Airbus A320neo. Officials in Toulouse recently expanded the jet’s capacity from 180 to 189 in a bid to close a gap in seat mile costs with the MAX 8. Sunday’s announcement once again gives Boeing the edge, essentially preserving the lead it had previously maintained.

The 737-8 has held an operating cost advantage dating back to the 737NG, where the 737-800 seated 160 passengers versus 148 for the A320. This capacity difference gave the Boeing aircraft a 6-7% advantage in seat-mile economics, which proved essential in its sales campaigns and shaping of public perception.

The high density version also begs questions of the future of the MAX 9, currently at a maximum capacity of 220. The MAX 8’s extension to 200 places the airplane reasonably close to the MAX 9. A move to expand the MAX 9 would not be unexpected, particularly given rival Airbus’ recent extension of the A321neo to 240 people. How exactly the company might accomplish such a feat is unknown, though Boeing could potentially follow Airbus in toying with door and emergency slide sizes to satisfy safety regulators.