If you're planning to travel to the United States this year, you may be given a green option with your car hire. Some of the largest rental companies are buying in hybrid cars in an effort to reduce their carbon footprint.

Hertz is planning to take delivery of 2400 hybrid cars this year, whereas Enterprise currently operates 5000, the largest hybrid fleet in the US. Avis currently owns 2500 hybrids, and it's predicted that the other major car hire companies will be following suit and buying in their own stock of the gas/electric fuel sippers.

Another benefit of these cars is that they are more economical on fuel. With current US gasoline prices at just $3 a gallon (working out at roughly 30p per litre), fuel economy may not sound all that important, but the majority of standard US cars are quite fuel-thirsty. But bear in mind that if you only plan on driving short distances then the standard car may work out better cost-wise as some car rental firms charge extra for their hybrid cars.

These extra charges can be as high as $24 per day, depending on the company, the length of hire, and where the rental firm is located. You may not always be able to specify a hybrid car, but it's always worth mentioning one when you book and then following it up with a phone call to the pick-up branch to check availability.

It may seem an unimportant part of car rentals, but for the environmentally conscious, the choice of a hybrid hire car couldn't come too soon.