The machine would monitor the temperature and increase the price of drinks as the weather heats up.

"This technology is something the Coca-Cola Co. has been looking at for more than a year," said company spokesman Rob Baskin, without giving precise details of the new machine.

The BBC's Mark Fisher: You may want to use a thermometer if you are planning to buy a drink on a hot day

Coca-Cola chairman and chief executive Douglas Ivester first mentioned the concept of the temperature-sensitive vending machine in an interview with Brazilian magazine Veja earlier this month.

"Coca-Cola is a product whose utility varies from moment to moment," Mr Ivester said.

He added that the new machine would cater to the basic law of supply and demand, as consumers' desire for cold drinks increases in hot weather.

"So, it is fair that it should be more expensive," Mr Ivester said.

"The machine will simply make this process automatic."

Mr Baskin said a computerised vending machine could vary prices according to other factors.

"What could you do to boost sales at off hours? You might be able to lower the price. It might be discounted at a vending machine in a building during the evening or when there's less traffic," he said.

The tests are a sign of the plummeting cost of technology, which makes it viable to install computer chips to determine prices of a relatively-cheap product.

So far there is no indication of how price and temperature might be correlated. Pepsi-Cola, Coca Cola's biggest rival, said it had not been testing such a machine itself.

A Pepsi spokesman said the idea sounded like a scheme to exploit consumers rather than benefit them.