The price of oil has been inexorably rising since last summer when it was $60 a barrel to its current level of around $135. This has forced most airlines into a series of hikes in their fuel surcharges.
The oft repeated theory is that air fares can only go so high before people stop flying.
But are there any signs yet that the price of oil is indeed affecting the level of business travel?
So far, perhaps surprisingly, there is scant evidence. If anything, it is pointing the other way, suggesting that business travel is holding steady.
There was an ominous start to the year when, amid much prediction of economic gloom, Hogg Robinson Group said that trading conditions were "challenging" and reported that demand was "softening" among SMEs and in its events division.
In March, when oil was well over $100 a barrel, a leading analyst from Carlson Wagonlit Travel warned there might be a travel freeze if fuel costs and therefore fares went on rising.
Dale Eastlund, director of air solutions for CWT in North America, said the crunch could come in the third quarter of the year when companies, because of rising prices, have spent their budget.
Then in May, as more and more airlines announced cuts in capacity, routes, frequencies and jobs as well as the scrapping of aircraft, Jean-Cyril Spinetta, chairman and ceo of Air France KLM, said oil prices would not only hit profits but also, if fares rose too much, deter people from flying.
But last month the pendulum swung back. A report from American Express and CFO Research Global Business and Spending Monitor found that the vast majority of businesses in Europe said they planned to keep travel at the same level or increase it in the next 12 months.
The poll showed that 88% of European businesses questioned said their domestic travel would remain as it is or grow while 80% said the same of their international travel.
A second fillip was the figures from the UK Guild of Travel Management Companies (GTMC) which showed that bookings by member agencies stayed steady in the first three months of 2008 and were 7% up on the same period in 2007.
The Guild said business travel in the country was "robust" – the same word Andrew Cosslett, ceo of InterContinental Hotels, used to describe business in the hospitality industry. There was little doubt that he still saw it very much as a seller's market.
There have been some words of warning from Anthony Grigson, executive general manager of FCm Travel Solutions.
He said the increasing cancellation of services and grounding of aircraft had "sparked a new era of 'dynamic flying' that is affecting schedules, costs and productivity for business travellers in many parts of the world – with the full impact yet to come."
He added: "The days of airlines flying half full are fast disappearing. They are now firmly focused on the return on investment for every seat and every takeoff, so we are now seeing reduced frequency on low-yield routes, as well as reduced capacity and onboard service on other routes.
"In some markets, bookings made up to a week in advance are no longer guaranteeing well-priced seats, and we're seeing more of our clients being forced to travel economy on relatively high fares.
"Reduced availability and higher fares, particularly on monopolised or highly frequented routes, are creating inconvenience for business travellers and blowing out their budgets.
“The corporate sector is also being affected by last minute flight cancellations, then waiting for hours before the next flight. Travellers now need to arrange their journey with the expectation that it may be disrupted on the day."
But his fears are not echoed by other travel management companies. Those to whom BTE spoke all said the impact so far had been minimal. One which replied that there was nothing to suggest oil prices were affecting travel levels, was typical.
With the price of oil having actually fallen in the past two days (July 7-8) by just over $5 per barrel, the worst may be over but please don't bet on it.
It might be that the crunch will not come until the autumn when travel budgets may be depleted.
But so far, it has not been anything nearly as bad as was feared.