Taking full advantage of the law of supply and demand, Coca-Cola Co. has quietly begun testing a vending machine that can automatically raise prices for its drinks in hot weather.

"This technology is something the Coca-Cola Co. has been looking at for more than a year," said Rob Baskin, a company spokesman, adding that it had not yet been placed in any consumer market.

But the potential was heralded by the company's chairman and chief executive in an interview this month with a Brazilian newsmagazine.

Chairman M. Douglas Ivester described how desire for a cold drink can increase during a sports championship final held in the summer heat. "So it is fair that it should be more expensive," Ivester was quoted as saying in the magazine, Veja. "The machine will simply make this process automatic."

The process appears to be done simply through a temperature sensor and a computer chip, not any breakthrough technology, though Coca-Cola refused to provide details Wednesday.

While the concept might seem unfair to a thirsty person, it essentially extends to another industry what has become the practice for airlines and other companies that sell products and services to consumers. The falling price of computer chips and the increasing ease of connecting to the Internet has made it practical for companies to pair daily and hourly fluctuations in demand with fluctuations in price--even if the product is a can of soda that sells for just 75 cents.

The potential for other types of innovations is great. Other modifications under discussion at Coca-Cola, Baskin said, include adjusting prices based on demand at a specific machine. "What could you do to boost sales at off-hours?" he asked. "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."

Vending machines have become an increasingly important source of profits for Coca-Cola and its archrival, Pepsico. Over the last three years, earnings of the soft-drink giants have eroded as they waged a price war in supermarkets. Vending machines have remained largely untouched by the discounting. Now, Coca-Cola aims to tweak what has been a golden goose to extract even more profits.

"There are a number of initiatives under way in Japan, the United States and in other parts of the world where the technology in vending is rapidly improving, not only from a temperature-scanning capability but also to understand when a machine is out of stock," said Andrew Conway, a beverage analyst for Morgan Stanley. "The increase in the rate of technology breakthrough in vending is pretty dramatic."

Machines are already in place that can accept credit cards and debit cards for payment.

In Australia and North Carolina, Coke bottlers use machines to relay, via wireless signal or telephone, information about which drinks are selling and at what rates in a particular location.

The technology is known as intelligent vending, Baskin said, and the information gathered and relayed by Internet helps salespeople to figure out which drinks will sell best in which locations.

In Japan, some vending machines already adjust their prices based on the temperature outside, using wireless modems, said Gad Elmoznino, director of the Trisignal division of Eicon Technology, a Montreal-based modem maker. "They are going to be using more and more communications in these machines to do interactive price setting," he said.

Industry reactions to the heat-sensitive Coke machine ranged from enthusiastic to sanctimonious. "It's another reason to move to Sweden," one beverage industry executive sniffed. "What's next? A machine that X-rays people's pockets to find out how much change they have and raises the price accordingly?"