As oil prices continue to rise, with no sign of a reduction anytime soon, more and more motorists are beginning to confront that most terrible of all questions: How am I going to afford to run my car in the future?

The days of cheap gasoline are gone forever and we now need to think seriously about ways of mitigating our fuel consumption and the gas mileage devices that might just help.

Obviously we need to keep our cars in tip-top running order. Even a set of old worn out spark plugs can cost you 5-7, tyres at too low a pressure 5. Add these together and it's clear that a well-maintained car should perform 14-18, and sometimes even more.

What's more, these gas mileage devices can be built from a number of easily and cheaply (under $100) sourced parts and installed by anyone with minimal DIY capability.

So how does it work? In a nutshell, it is a simple, high output electrolytic cell, the output of which (a hydrogen-oxygen complex known as Brown's gas) is fed into the inlet manifold of your car. They use electrical energy from the alternator that would otherwise go to waste because, in modern cars, the battery is kept well charged by the alternator within the first few miles of your journey.

The secret of this system is that it runs alongside and complements the gasoline technology with which we are all so familiar.

Are they effective? Well, several thousand of these systems have now been installed and as far as we know, no one has reported a complete failure to work. The reported performance does vary a lot, however, the minimum improvement in mpg that I havee seen is 6%, in a 200X Nissan Micra. There have been many claims of a doubling in miles per gallon, mostly in big-engined US-built autos. Probably a bit of over-exaggeration is creeping in here. Fifty percent is more likely.

And are there any other benefits? The developers of this system claim that engines run much more cleanly because of the improved combustion that takes place within the engine. This is quite possible and could potentially lead to reduced servicing costs in the longer term.

Are there any downsides? None as far as we can see. The developers maintain that it cannot invalidate the manufacturer's warranty on a new car and that the system can easily be removed if necessary with no damage to the car at all.

At the current rate of development, it's going to be several years before a true, fully hydrogen powered car hits the road so, while we wait, it seems prudent to make use of this 'halfway' technology to save gas mileage. Actually, 'halfway' is doubly appropriate; if you could drive half as far again on each gallon of gas, try calculating how much money you'd save in a year. I bet it's at least ten times the cost of the guide and the gas mileage device parts combined.