Boeing is exploring a potential market of over 1,000 aircraft in a niche between its single-aisle 737 and wide-body 787, but has not decided whether to invest in a new jetliner, its sales chief said on Sunday.

Airlines have told the planemaker they are interested in something about 20 per cent bigger than its out-of-production 757 and able to fly further, putting it beyond the reach of the latest A321LR single-aisle offering from rival Airbus, he said.

Speaking in an interview ahead of the Paris Airshow, John Wojick, senior vice president for global sales and marketing at Boeing Commercial Airplanes, said airlines were looking for an jetliner able to seat about 240 people with greater comfort, but just as efficiently as the smaller 737 workhorse.

"That is the secret sauce. If we can find a way to do that, we think we would have a really effective plane in the marketplace," Wojick told Reuters.

The last 757 was delivered in 2005, but remains popular with US airlines because of its range and performance, while its larger contemporary, the 767, is being replaced by the 787 Dreamliner.

Many 757s will soon come up for replacement.

"We sold over 1,000 757s and several hundred 767-200s so it would make sense that (the market) was at least that big," Wojick said, adding there would also be growth on top of that.

The market is "certainly more than 1,000," he said.

Wojick declined to comment on how many orders Boeing expects to announce at this week's air show, but said it would be "tracking toward" the full-year target by the end of June.

The remark implies that Boeing expects to make announcements involving some 200 aircraft at the show, which starts on Monday.

Boeing has said it aims to book orders in 2015 at least matching deliveries, which it estimates at 750-755 aircraft. It goes into the show with 175 orders, or 131 after cancellations.

Despite an industry-wide dip in volumes after record orders, demand for wide-body and other jets remains strong, Wojick said.

Boeing is working on more potential orders for the freighter version of its 747-8 jumbo, buoyed by recent improvements in cargo markets, he added.

He said demand for the fuel-saving 737 MAX had not deteriorated as a result of lower fuel prices. He also denied any significant price pressure on the 737 or 777, saying any pressure on 737 pricing came from the competition, not fuel.

On production, Wojick said Boeing is still working out the details of the transition between the current version of its 777 mini-jumbo and the revamped 777X.

"Through 2016 we are doing 8.3 (777s) per month," he said.

Beyond that, there would be a "normal transition" between models. Boeing has expressed confidence it can avoid cutting production of the current 777 version. – Reuters