The following questions will help you to decide if the vehicle should be petrol, diesel or alternatively fuelled and also provide information to help make a decision about engine size/configuration.
Don't confuse engine size with power or performance. While historically there has been a relationship between the two, many modern vehicles use turbo chargers, super chargers, (sometimes both combined) and electric motors to provide much more power than one would expect from a small engine. You should consider the number of passengers, load and length of journeys, as well as where the vehicles will primarily be driven.
Use historic information or ask business managers about current journey types, frequency and also whether these patterns are due to remain constant for the foreseeable future.
Where will the vehicle be driven?
Mainly motorways, town centres or a combination? Diesel vehicles are better suited to motorway and 'A' road journeys, but hybrid (petrol/electric) vehicles are much better suited to urban stop-start driving environments. Does the vehicle have to go off-road, and if so is this just dirt tracks or harsh rough terrain? Many 'soft road' vehicles are adequate for farm tracks and fields, but for remote harsh environments proper off-road vehicles such as Land Rover Defenders may be an essential requirement.
What is the length of the journeys?
Petrol engine cars are often more cost effective for frequent short journeys and diesels pay for themselves when being used on long motorway routes (diesels have a purchase cost premium but tend to be more fuel efficient than a petrol model).
How often are the various journeys carried out?
Carry out some analysis on recent trends, and estimate journey profiles if accurate information is not available. This could be done by taking a sample of vehicles and getting estimates from the drivers or their managers.
Don't go for the worst case scenario as it could be an expensive solution. How much extra are the lease rentals for that 1.9 litre diesel TDI than the petrol 1.3 litre?
