There's some simple maths when it comes to airfares: the higher the price, the bigger the profit.

And the most expensive tickets tend to be those sold at the very last minute - specifically those picked up by business travellers with schedules dictated by sudden deals and unexpected client meetings.

And not coincidentally, these fares are usually paid for by the company, Bloomberg reports.

It also turns out there are some marked differences in buying habits among industries, according to data released Thursday by Concur Technologies, which analysed 25 million airline ticket sales last year across nine industries.

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Perhaps unsurprisingly, those in professional service fields, such as law and consulting, bought more than a quarter of their air tickets within three days of a trip, the largest segment.

That makes for some pretty pricey seats.

Media was next, at 20 per cent - since news events often tend to erupt without warning.

At the other end of the spectrum is higher education, with 68 per cent of tickets in that field being sold 15 or more days before a trip.

The big spenders when it comes to air travel. Photo / Bloomberg
The big spenders when it comes to air travel. Photo / Bloomberg

Industries such as energy, financial services, manufacturing, and technology fell in the middle of the spending pack.

Airline tickets booked less than a week before departure are 44 per cent more expensive, on average, than the same ticket booked 15 or more days in advance, according to Concur, which sells corporate travel and expense-reporting services. (German software giant SAP acquired Concur in 2014).

Airlines manage their inventories to hold some seats open on most flights for corporate travellers.

They're also keen to sell as many last-minute tickets as they can, a lucrative category the industry terms "close-in bookings" and which tend to yield fatter margins.

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These tickets are critical to a carrier's overall financial health. US airlines suffered an almost two-year revenue swoon starting in 2015, with weak pricing power eventually spreading even to last-minute tickets.

Some carriers, meanwhile, set fares for same-day tickets the same as those sold far in advance - a huge bonanza for business travellers.