What is LPG, and is it worth converting?
LPG (Liquefied Petroleum Gas), sold at forecourts as "autogas," typically costs around 75–85p per litre compared to 155–160p for petrol. That's a tempting gap. But LPG contains less energy per litre, so you use more of it. Conversion costs £1,000–2,500. And the forecourt network is shrinking. Here's the honest maths.
The real cost per mile comparison
LPG has a lower calorific value than petrol, roughly 6.9 kWh/litre vs 8.9 kWh/litre. This means a converted car consumes approximately 15–20% more LPG by volume to travel the same distance as on petrol. The fuel savings are still real, but smaller than the raw price difference suggests.
Even accounting for the higher consumption, LPG typically saves around 40% per mile compared to petrol at current prices. At 15,000 miles per year with an average fuel economy of 35 mpg equivalent, a typical driver could save around £800–1,000 annually.
The break-even calculation
With a mid-range conversion costing around £1,800 and annual savings of £900, the break-even point is around 2 years. That assumes consistent high mileage and the availability of LPG on your regular routes. Every vehicle, usage pattern and local fuel price is different. Run the numbers for your specific situation before committing.
The UK's LPG network has shrunk significantly as electric vehicle investment has dominated forecourt development. While there are still ~1,400 stations, they're not evenly distributed. Rural areas in particular may have long gaps between LPG pumps. Check the Autogas Live map before converting to confirm your regular routes are covered.
Is LPG right for you?
| Factor | LPG suitable? |
|---|---|
| High annual mileage (15,000+ miles) | Yes, savings add up |
| Regular motorway / long routes | Yes, better range per tank |
| Urban-only short journeys | No, break-even takes too long |
| Planning to keep car 5+ years | Yes |
| Rural area with poor LPG coverage | No, range anxiety risk |
| Car valued over £5,000 | Possibly, better conversion ROI |
What LPG conversion actually involves
A proper bi-fuel LPG system installs a secondary fuel tank (typically in the spare wheel well or boot), an LPG-specific injector rail or mixer, a vaporiser that converts liquid LPG to vapour at the correct pressure, and software modifications to the engine ECU. The car starts on petrol and switches to LPG automatically (or manually via a dashboard switch) once the engine reaches operating temperature. Good quality conversions by UKLPG-approved installers are seamless in normal use — the switch happens without driver input and performance is broadly similar on either fuel.
Conversion quality varies significantly. A budget installation using low-grade components can cause poor fuel economy on LPG, rough running, or long-term engine issues from inadequate fuel mapping. The UKLPG approval scheme certifies installer competence and component quality. The price difference between a budget conversion (£800–1,000) and a properly approved installation (£1,500–2,500) is almost always worth paying, particularly given that a poor conversion can cause more than the cost difference in problems.
Insurance, MOT and practical considerations
You must declare an LPG conversion to your insurer. Most mainstream UK insurers accept it without a premium increase — LPG vehicles have a good safety record — but some may add a small surcharge or request a certificate of compliance from the installer. Failing to declare it could invalidate your insurance in the event of a claim.
The LPG system is checked as part of the annual MOT: inspectors look for leaks, secure tank mounting, and correct labelling. UKLPG-approved installations are designed to pass. The LPG tank itself requires periodic retesting under pressure regulations.
Day-to-day practicalities are manageable but real. Most UK LPG forecourts use a bayonet-style nozzle connector; carry an adapter for the older ACME thread connector, which some rural stations still use. Boot space is reduced by the secondary tank. Some LPG pumps require a pre-registered fuel card rather than card payment at the pump. None of these are dealbreakers for high-mileage drivers where the economics work, but they are worth knowing before committing to a conversion.
For high-mileage drivers considering a major investment in alternative fuel, a secondhand EV with home charging may now offer better long-term economics than LPG, particularly as the LPG network continues to contract. Worth modelling both before deciding.