I buy the same brand of petrol but not always at the same station. I buy a Woolworths card from a seller who gives 5% off at time of purchase, so I'm already ahead savings wise. Some of the money on the card is used for groceries (buy over $30 and the 4c off per litre deal kicks in). This is then used for more money off when actually buying the fuel.
I tend to use the one service station now as I've found the petrol from the 4 cents offer from one particular supermarket does not drive my car further so as soon as I realised this, started to use the independent one which is usually cheaper than the 4 cents offer anyway and I get better fuel consumption as well.