RickW: You guys are lucky, There is pretty much no price competition in Christchurch that I've found apart from npd in Hornby which has diesel 18c cheaper.
Last time I was in Christchurch, that NPD was the only place that had petrol at a price cheaper than the "national price"
Here in Dunedin, Pak N Save Fuel is 2c cheaper than the "national price", as is the Mobil down the road and Challenge in Caversham is 1c cheaper.
Otherwise its all the same at every store
I was amazed when I travelled from Wellington to Palmerston North in late 2014 and saw such a price difference between stations