Oil companies dont make much on the fore-court, its a matter of pence with most of the cost coming from tax as Rich said. Teh oil company record profits are made from exploration and other activitivities and products they crack off of the crude.
The cost of our petrol is affected by two factors, the diesel cost is inflated due to the over-demand for diesel now-adays, as our aging refineries dont produce as much diesel as required, as when they were built diesel wasnt used in commercial vehicles in the volume it is today. And if you remember that petrol used to be cheaper than diesel, that was due to over production as people switched to diesel. But the lazy yanks figured out they could import our refined petrol cheaper than they could import crude and refine it so started buying our petrol excess inflating the petrol price again!
And then the goverment tax us every which way on the small amount that petrol actually costs, not sure if people remember the last oil crisis iirc the goverment made an extra 50million in tax than expected due to price increases, and then still increased the tax to raise even more.