The world's two makers of large commercial passenger aircraft Monday both presented their market forecasts through 2018 at the Paris air show. Boeing projects commercial airline demand of $1.38 trillion for 20,150 new passenger and cargo planes over the next two decades. Airbus projects a market for 15,518 airplanes with a value of $1.29 trillion over the same period.

Airbus expects average annual growth in air traffic to be 4.98 per cent, while Boeing predicts 4.7 per cent average growth. By comparison, Airbus says that air travel grew an average of 4.7 per cent annually from 1988 to 1998. It grew 6.1 per cent in 1997 and 3 per cent in 1998, according to Boeing. Air traffic is measured in revenue-passenger-kilometers, or the number of revenue-paying passengers for each kilometer an airlineflies.

``There seems to be a more pronounced separation in forecasts than we've seen before," said Brian O'Keefe, aerospace analyst at Commerzbank AG in London.

The two companies start their projections from different bases. Boeing, which includes planes as small as 50 seats in its analysis, counts a total world fleet today of 12,600 planes, while Airbus counts 10,000 planes, in part because it counts only planes as small as 70 seats. Airbus sees a replacement market of 5,650 planes over the next 20 years, while Boeing sees a replacement market of 4,330 planes. As a result of additions and replacements, Boeing projects a world fleet of 28,400 planes in 2018, while Airbus foresees only 19,106 planes.

The biggest difference between the two plane makers' projections is their expectations for the market's composition in terms of plane size. Boeing is more bullish on small and midsize planes, while Airbus sees relatively more promise in very large aircraft with more than 400 seats.

Boeing currently ownsthat market with its 747 family, but Airbus is considering developing an even larger jet with upward of 550 seats, known for now as the A3XX. Airbus has said it plans to decide by the end of the year whether to proceed with that risky and costly project.

Airbus predicts a market for more than 1,200 passenger planes with more than 400 seats over the next 20 years, said Adam Brown, Airbus vice president for forecasting and strategic planning, who presented the company's global market forecast. Airbus Managing Director Noel Forgeard said Sunday that he sees a total market, including cargo, for 1,500 of the proposed superjumbo jets. Mr. Brown noted that while Airbus has cut "significantly" from last year's projection its growth forecast for ``a number of key markets serving the Asia-Pacific region'' and has projected an increased dispersion of flights onto secondary routes, the plane maker has only slightly reduced its demand forecast for planes above 400 sets. ``This shows that demand for this new category ofvery large and economical aircraft will prove to be very robust in the face of changing market conditions,'' he said.

Airbus predicts demand for 560 planes in the 500-seat category, 372 planes in the 600-seat range, 228 planes in the 800-seat category and 48 planes in the 1,000-seat range. The largest passenger planes today are high-density 747s, of which there are 48 with an average seat count of 546.

Boeing sees demand for 933 planes with more than 400 seats over the next two decades, out of which it sees demand for 360 planes with more than 500 seats, said Randy Baseler, Boeing vice president for marketing in its commercial airplane group.