If petrol stations were made to publish their current prices along with their GPS coordinates, it would be easy to show on a map the locations of cheap petrol nearby. It would also be possible to calculate how far you would have to drive to get cheap petrol and whether it was worthwhile. Using that information, you could recommend a place to go for the best deal on your petrol. Couple that with your car's fuel gauge and you'd be able to automatically pop up a recommendation to buy fuel when it's cheap and nearby. If your car's computer can analyse both your driving habits and the petrol price cycle, it could help you optimise your purchases for the cheapest, most efficient and timely outcomes, and the only thing you'd need to see would be a slight deviation in your GPS guidance with a note to buy fuel now.
And that is why petrol stations do not publish their prices online unless forced to do so. They know that a large portion of their business comes from necessity: you need fuel now, and they're the only one nearby. Sometimes their prices will be high and you get screwed. They're okay with that. But if you're able to predict and take advantage consistently when prices are low, that's not okay by them. Anything, such as easier access to current prices, that helps you make better decisions as a consumer puts the brakes on their gravy train. They'll cry poor. They'll tell you it's not fair. They'll even try to tell you it's not possible. All lies.
Mokalus of Borg
PS - Well, maybe it's not fair.
PPS - But only if they stick with their current price practices.