But it's still useful to know about price variation so that you can plan ahead. I regularly drive past several different petrol stations, and if I know that one of them is usually cheaper or usually more expensive then I choose to use or avoid it, or to decide that I'll fill up tomorrow when I'm going that way rather than today at a more expensive one.
And that'd be more useful built into satnav, so that if I know I have to fill up somewhere along my route then I can pick the cheapest place, since there's no real time cost to any of the options compared to each other.
It's interesting running the numbers though. e.g. if it only take 10 minutes to get cheaper fuel, how much cheaper does it need to be for your time to be worth more than the UK minimum wage (£12.21 for adults over 21)
based on my maths (from above calculations) it needs to be about 7p per litre cheaper to justify the extra 10 minutes and for your time to be worth more, per hour, than the minimum wage.
7p cheaper for 10 minutes works out at about minimum wage if you're buying 30 litres, but with a bigger car you could easily be buying twice that, which works out much better.
Although of course you also need to factor in how much fuel you burn driving to the cheaper place, and the extra wear and depreciation on the car. If you take the HMRC standard rate of 45p/mile (which was meant to cover all of that kind of thing, but hasn't been updated for years) then even going a few miles out of your way quickly ends up costing more than it's likely to save.
A 7p per litre difference does sound like the difference between local station and motorway prices though, and they probably will have factored in that opportunity cost of time...
Only 7p?
Motorway services have shocking price markups, way more than 7p. Most people don't realise this or are just too lazy to find something that isn't quite as convenient.
According to the live feed at https://www.rac.co.uk/drive/advice/fuel-watch/ I see:
Unleaded is 131.80p (UK wide) and 156.80p (Motorway Service Area).
That's nearly a 20% markup.Last time I drove into a motorway services and saw prices ~20p/litre higher I just drove through the petrol station and found a local garage to fill up at.
Spending an extra £10 once or twice a year when driving a few hundred miles and thus needing to fill up at a motorway is nothing. Chances are I’m spending that much on an overpriced coffee when I do that anyway.
Ironically I had to do a small topup on the M4 today, and yeah, that was mad!