It’s hard to fathom the sheer tonnage of fuel used by air travel. Today’s official announcement by the Boeing Company board that the 737 family will be re-engined, creating a line of 737REs, is frequently being described in terms of percentages: “The U.S.-based manufacturer expects the 737RE’s 737 MAX‘s fuel burn to be 16 per cent lower than the current A320 family and 4 per cent lower than the A320neo family.”

You start getting more of an idea of the scale when Boeing says: “When compared to a fleet of 100 of today’s most fuel-efficient airplanes, this new model will emit 277,000 fewer tons of CO2 and save nearly 175 million pounds of fuel per year, which translates into $85 million in cost savings.”

Counterpoint: Airbus head John Leahy shoots back, “Once again, Boeing is in denial. The re-engined 737 cannot possibly match the fuel efficiency and maintenance cost savings of the A320neo family.” Boeing claims to have 496 orders in hand already, so at least a few airlines are willing to make the bet that Boeing can compete. Squishily, from an engineer’s perspective, Boeing points to improvements in fuel efficiency of “up to” seven percent since its Next Generation 737s launched in 1998.

The new boost will be due simply to strapping on new CFM International LEAP-1B engines and calling it good. (The Airbus A320neo will also use a LEAP engine, but CFM has optimized the 1B for Boeing’s use.)

Looking at the company functionally, besides its planes, Boeing primarily flies fuel around the world. Secondarily, in terms of weight, come passengers and other cargo. The Boeing 737-600, itself an advance in fuel efficiency, can carry some 46,000 pounds of jet fuel…and 132 passengers. (If the passengers are 200-pounders, that’s 33,000 pounds.)

Boeing’s earlier fuel-savings estimates were based on a 100-plane fleet, but the company is also forecasting demand on the order of 23,000 737s over the next 20 years (nearly $2 trillion in sales). That’s 40,250,000,000 pounds of fuel saved annually. A percent here and there really starts to add up.