Petrol, Diesel and Alternative Fuel: A Guide

Petrol and diesel prices are rising all the time. The new fuel tax increase will add one pence to the price of fuel in April 2010, October 2010 and again in January 2011.

Choosing between a petrol or diesel engine can be confusing, and that is before you add in the growing number of plug-in hybrid and electric cars being introduced into the market.

Below is a quick guide on the benefits and drawbacks of each type of fuel.


Information: Petrol is the most popular fuel with motorists in the UK and is widely considered to offer better performance and a quieter drive.

Types: There are four main types of petrol; unleaded, super unleaded, leaded replacement petrol (LRP) and high performance.

Unleaded is the most common type of petrol used today. Super unleaded and high performance are more expensive variants offering better performance, while LRP is generally used only for less common vintage vehicles.

Efficiency: Petrol engines are usually considered to be less efficient than diesel alternatives. Typically – although this isn’t an exact science – a petrol engine will return less miles to the gallon than a similar sized diesel engine.

This will of course mean more visits to the pumps for a petrol engine. However, diesel is generally more expensive than petrol at the fuelling station by a few pence.

Emissions: Compared to diesel, hybrid and electric engines, petrol engines generally have higher CO2 emissions.

Cost: Petrol is cheaper than diesel at the pump, usually by a few pence. Over the lifetime of a car this can certainly add up. However, higher CO2 emissions could mean higher road tax, which is based on a car’s CO2 emissions.


Information: Diesel engines are increasingly popular thanks to the efficiency and lower CO2 offered over petrol alternatives. However, diesel engines are noisier than petrol engines and offer a less smooth ride.

Types: There are high performance variants of diesel fuel, but they are quite rare.

Efficiency: Diesel engines are more efficient than petrol alternatives. They offer higher miles per gallon and less gear changes.

Emissions: Recently, diesel models of popular cars such as the Ford Eco:DRIVE range, the Alfa MultiAir and the Renault Airdream+ range have further increased the efficiency of diesel engines and cut CO2 emissions.

Price: The lower CO2 emissions from diesel engines could result in a lower road tax as it is calculated using the CO2 emissions of an individual model. Added to the increase in fuel efficiency, the more expensive price of diesel fuel could be offset by the savings when driving the car.

Cost: Diesel costs more at the pump than petrol, and diesel models generally cost more than petrol models to buy. A buyer will need to work out if the higher miles per gallon and potential tax reduction will offset the higher purchase cost.

Diesel engines are more expensive to service and repair than petrol models.

Residual values of petrol and diesels

As stated above, petrol engines are generally cheaper to repair. Despite this, diesel engines tend to keep their value longer as more buyers look for lower CO2 and more efficient vehicles.

However, residual value depends on the model, mileage, condition and many other factors as well as the type of fuel the vehicle used.

Plug-in hybrid and electric

More and more manufacturers are embracing hybrid and electric cars. The plug-in hybrid Vauxhall Ampera is due to arrive in 2012 and Ford recently announced plans for five new hybrid or electric models.

Plug-in hybrids: Plug-in hybrids are a combination of a petrol engine and an electric motor.

A plug-in hybrid is usually capable of driving using just the electric motor for short distances of around 10 miles at a reduced speed. As it is powered via an electric socket and doesn’t use any fuel, it is known as zero emissions driving.

Once the charge runs low, the petrol engine can power the electric motor to extend the range of the car. The Vauxhall Ampera, for example, can travel 10 miles using electric power and a further 340 miles using a combination of petrol and electric.

Plug-in hybrid cars generally have high miles per gallon (or mpg) and lower emissions than petrol and diesel models. However, the major issue with plug-in hybrids is the price. As the technology is relatively new, the cars can be expensive. Similarly, there isn’t much of a charging infrastructure in the UK at the moment for recharging.

With a plug-in, this is not too much of a problem as the petrol engine can be filled up instead.

Electric: Electric cars are ‘zero emission’ driving. They use batteries – usually lithium ion – to power the vehicle without the need for petrol, diesel, or any other type of combustion engine.

Electric cars are cheap to run and charge, and many believe they will be the future of the motor industry.

But – and it’s a big but – they are still in their infancy. Electric cars are very expensive because of the cost of the battery, and there is little information about warranties and battery replacement costs.

There is also the problem of a lack of infrastructure. Electric cars need a network of charging points which isn’t available yet, although the UK government recently announced a number of initiatives to improve this, including test schemes in four different areas.

Similarly, a home charging station could cost as much as £2,000 to install.

On the plus side, drivers or electric cars will not pay road tax or congestion charges and from January 2011, an incentive scheme will offer up to £5,000 off electric vehicles.

The range of electric cars is in question, with many only capable of travelling up to 100 miles before they need to be recharged – something that could take up to eight hours to do.

Electric cars are cheap to run, but there need to be large advances before they realistically challenge petrol and diesel for dominance.