Dr Bertrand Piccard and Mr Brian Jones, due to pick up a million-dollar prize for becoming the first to fly non-stop round the world in a balloon, will face a £2.5 million bill for their record bid, according to experts.
While the Swiss watchmaker Breitling, which sponsored the flight, has refused to divulge the costs of the expedition, Mr Don Cameron, the British designer of the Breitling Orbiter III, said balloons of that type were worth between £575,000 and £2.3 million.
Mr Cameron, speaking at the flight control centre in Geneva, said the balloon which took Dr Piccard, a Swiss psychologist, and Mr Jones, a British ballooning instructor, round the world in 19 days, 21 hours and 55 minutes, was the most advanced he had made. Added to this sum will be the cost of on-board equipment for the pressurised cabin, navigation instruments, survival gear and general supplies.
The sponsors, organisers and pilots will also have to pick up the bill for transmissions between the balloon and the control centre, and for the authorisation costs for overflying some 20 countries.
Dr Piccard and his team had to make various trips to China to gain permission to use its airspace. Beijing had banned balloon flights over its territory after Mr Richard Branson overflew it without permission in his own record bid last year.
Balanced against these costs is the one million dollars of prize money on offer since 1997 from the US brewery Anheuser-Busch to the first balloon crew to fly round the world before the end of the 20th century.
Some of the expedition's services also came free of charge, such as the work of two expert meteorologists, Mr Luc Trullemans of Belgium and Mr Pierre Eckert of Switzerland. They said they had worked on the project free of charge out of their friendship with Dr Piccard.
Other costs include the hire by the Swiss watchmakers of a plane to fly over the balloon yesterday as it landed in the Great Sand Sea desert of south-western Egypt. The plane carried numerous photographers whose pictures will be distributed free of charge.
Unlike his previous two Breitling-backed round-the-world bids, this time Dr Piccard's flight was not backed by the International Olympic Committee (IOC), which has recently been dogged by corruption allegations. A source close to the IOC said that Swatch, another Swiss watchmaker and partner of the IOC, had demanded that the IOC logo of five interlaced rings not be associated once again with the company's rival, Breitling.