HUGE savings are potentially available for fleets that switch from petrol to diesel.

A firm running 150 vehicles could save £400,000 on fuel over three years by switching to diesel, according to fleet management firm CLM.

But fleets should take care to factor in higher front end costs and varying residual values across different types of car.

CLM analysed a customer’s fleet and found it was possible to save 25% in fuel by switching the bulk of the fleet to diesel and operating them for a lifecycle of three years/90,000 miles.

The evaluation was based on the mix of company cars the fleet operated, including the Audi A4, BMW 3-series, Volkswagen Golf and Passat, Ford Mondeo and Mercedes C-class.

The diesel cars averaged 48.7mpg compared to 35.7mpg for their petrol-engined counterparts, equivalent to savings of £2,750 per vehicle over a 90,000 mile fleet life. CLM managing director Tony Hulatt said: ‘Our analysis was based on fuel costs only, and didn’t take into account front end, holding or other wholelife costs.

‘But we were able to prove quite clearly that there are some very considerable savings in fuel costs to be made for fleet operators in switching from petrol to diesel.’

Jeff Knight, forecast manager for residuals experts CAP, said there were potential savings to be made, but fleet managers needed to do their homework before taking any action.

‘Just to view it as a broad brush is perhaps not the way to look at it,’ he said.

‘When both petrol and diesel vehicles come back to the used market, some will be more desirable than others. It might end up costing money to plough into diesel.’

Knight said superminis might not add up due to little difference in used petrol and diesel models. However, larger diesel cars with improved mpg and better RVs could be worth considering.

‘You must do your sums,’ Knight concluded.

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