Spot buying is not an alternative to a managed travel programme, consultant Richard Plummer told a meeting of the Belgian Association of Travel Managers in Brussels.
Mr Plummer, senior partner with the Corporate Travel Partnership, told more than 100 delegates that it should be part of a managed programme.
He said he was "absolutely against letting people do their own thing" as companies had to have some control and there were health and safety issues to contend with.
But he told the event, which was organised in conjunction with the Association of Corporate Travel Executives, that he supported "managed spot buying."
"Spot buying requires more control than a deal. Doing a deal is easy. But for spot buying you need a good travel management company and good commitment," he said.
It was most effective on either domestic routes or on short haul. It was not for long haul routes to New York or the Middle East.
"The spot market is specific and it really depends on your company culture and how savvy your travel bookers and TMCs are. It depends on how nimble they are," Mr Plummer said.
"There are certain routes where you need a deal because the company needs to guarantee its seat on a flight, for example London-New York.
"But there are a lot of flights where spot buying is a real alternative but you have to watch the market.
Michele Dauwe, managing director for American Express Business Travel for the Benelux countries, said for spot buying, it was important that companies were ready for change.
"What ever the TMC and the traveller are willing to do, if the company is not ready, nothing will happen," she said.
But she also warned that the more a corporate went to one particular destination, the more essential a deal was. "If you are very concentrated on a destination, you had better have a deal for it," Ms Dauwe said.
* See BTE Analysis