The inexorable rise of Toyota’s hybrid Prius will fuel speculation that the Japanese carmaker could soon be officially ranked the biggest in the world.

American sales data show that last year more Prius cars, with their petrol-electric engines, were sold than Ford Explorer sports utility vehicles. The Explorer has been the US’s best-selling SUV for the past ten years.

Prius vehicles are a relatively small part of Toyota’s overall production but, as the best-known mass production hybrid, the Prius has helped to elevate Toyota as a brand.

When General Motors releases its sales and production figures for last year it will be clear whether Toyota has pushed it out of the top slot – the first time GM will have been toppled for more than 70 years. Toyota said this week that its global sales climbed 6 per cent last year to 9.37 million and that its output was 9.5 million, up 5 per cent on the previous year. It is aiming to make just under 10 million cars this year. GM is expected to unveil its figures at the Detroit Motor Show, which opens tomorrow.

Toyota overtook GM for quarterly sales early last year but the US company caught up so the end picture isI not yet clear.

Toyota’s accession to the No 1 slot would underline the growth of Asian carmakers and be particularly symbolic if it occurs at the US’s biggest motor show, held in the heart of the American car industry. It is thought that GM will struggle to match Toyota largely because of weakness in its domestic market. But after cost-cutting GM has insisted that it has the cash to keep pace with Toyota. The company is to step up efforts to sell more cars overseas. Rick Wagoner, chief executive, has said that 75 per cent of sales will come outside the US within ten years. At the moment just under 60 per cent of vehicles are sold overseas.

The carmaker will make more of a push into the emerging markets of Asia, Russia and South America. Only four years ago the US accounted for the majority of GM’s sales.

In the US, the rise of Toyota’s Prius, which enjoyed a 69 per cent sales jump last year, has been partly triggered by high fuel prices. Toyota first started selling the Prius in the US in 2000. Meanwhile, the Explorer sold less than a third of what it achieved at the height of its popularity eight years ago.

Ford will unveil a more fuel-efficient version of the Explorer at the Detroit show. It is expected that the eight cylinder version of the vehicle will be shelved.

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