You are confusing petrol forecourts with extraction of resources. Petrol forecourts are an irrelevance here, it isn't where the money is being made. Firstly most forecourts are franchises (EG being the biggest owner) but anyway, that is a distraction
The extractors sell in fuel exchanges like the European Energy Exchange, the market here dictates the price of fuel to the energy generators at power stations etc
Extraction companies like Shell can't sell at anything other than the market rate for two main reasons, the market is there to regulate the prices and secondly the boards of directors have a fiduciary responsibility to their shareholders and selling off exchange below the market rate would absolutely leave them open to being sued by the shareholders (that's likely to be you and I if you have a pension) for not looking after the shareholders interests. That is why recovering their excess profits must be done by a statutory instrument like a windfall tax as that absolves the Boards of Directors from their responsibilities.
If journalists were being responsible, they'd explain all that but no, they put a picture of a shell forecourt in the image because its easy