The petrol against diesel debate shows no sign of cooling off and it's easy to understand why.

Petrol engines are continuously evolving and so are diesel engines - and, above all, the fuel price, which plays a major role in the debate, is jumping around (mostly upwards).

Looking at the latest crop of engines, and bearing in mind the unmistakable long-term trend in the fuel price, which would be the wisest buy- petrol or diesel ? Let's compare the two on certain vital points.

Purchase Price

Petrol is the clear winner on this point. A list of new vehicle prices will show that a diesel-engined car is between R10000 and R30000 more expensive than a directly comparable petrol-engined one from the same manufacturer.

This represents a difference of about 12percent to 15percent in price.

A diesel engine, with its higher compression ratio and very sophisticated injection and turbocharging equipment, is simply more expensive to build than a petrol engine of the same size.

Fuel Consumption

Here diesel is the undisputed winner (and this is the main reason why the petrol against diesel debate is still percolating).

Comparing fuel consumption data on cars with similar engine sizes from the same manufacturer shows a definite advantage for diesel in every instance.

Typical examples are:

BMW 320d: 6,9 l/100km against BMW 320i: 9,1 l/100km

Hyundai Getz 1,5 CRDi: 5,7 l/100km against Hyundai Getz 1,4 HS: 8,0 l/100km

Toyota Auris 2,0 D-4D: 6,6 l/100km against Toyota Auris 1,8 RS: 8,8 l/100km

These figures are for the standard mixed cycle of urban and highway driving. On a car used mainly for city driving the difference will be even bigger.

The nature of diesel combustion and the ability of a diesel engine to operate on very lean mixtures when no torque is demanded of it (such as when idling) makes it inherently more economical than a petrol engine.

Diesel owners will forgive their cars for a lot of shortcomings when they pull up at the fuel pump.

Assuming that fuel prices will on average be 10percent higher than today, and using the mixed-cycle data above, diesel owners can expect to save about R1800 on fuel costs for every 10000km travelled.

After 120000km that will amount to a savings of almost R22000.

Maintenance

Diesel engines, especially turbo-diesels, require more skillful maintenance than their petrol counterparts.

Oil change intervals on a diesel are also shorter than on a petrol engine, though that is changing with the introduction of low-sulphur diesel fuel.

Longevity

An evenly-contested point, but a turbo-diesel is going to come second, unless it has been scrupulously maintained and driven with due regard to its special requirements.

Driver Satisfaction

One driver's satisfaction is another driver's frustration. If you like an eager, rev-happy engine with scintillating performanc, go for petrol.

If you prefer a more relaxed driving experience, provided by an engine with plenty of torque at low revs (which makes for fewer gear-changes), diesel should be your choice.

Resale Value

Here the advantage has to go to petrol, simply because a petrol engine is more tolerant of abuse than a turbo-diesel.

Unless you really know how a turbo-diesel has been treated and maintained it should be regarded with a healthy dose of caution.

In conclusion, the choice between petrol and diesel remains a case of "horses for courses".

Otherwise, especially if you reckon you can shrug off the fuel price, go for petrol.