"Consumers are paying through the nose for petrol today, and they’re really angry," said Public Citizen president Joan Claybrook, who last week urged consumers to back proposed federal legislation that would require petrol pumps to take account of fuel’s tendency to expand in warm temperatures.

Because of the so-called hot-fuel phenomenon, she added, "this summer just about everyone will be overpaying for the petrol that they purchase." Claybrook said the temperature hit could cost customers an extra $3 billion (Bt96 billion) nationwide. In fuel-hungry California, where the statewide average petrol price passed the $4 per gallon mark on Thursday, a new survey showed that motorists could be overpaying by as much as $3.4 million a day during the summer months.

"It’s a significant number, and one that we shouldn’t be paying," said Judy Dugan, research director at Consumer Watchdog, formerly called the Foundation for Taxpayer and Consumer Rights. "With every rise in the price of petrol, hot fuel becomes a more important issue." For consumers and companies struggling with their fuel bills, the added insult of a hot-fuel penalty is unwelcome.