CNG seems to be a uniquely kiwi thing, for here it's been LPG. It used to be only used in taxis when first introduced about 25 yrs ago but now very common in private vehicles; particularly large ones; 4WD's, 6 & 8 cylinders. There used to be problems with the first generation of LPG cars blowing up...problem was if the tank was overfilled there was no room for expansion, so now they make it so the tank can't be filled more than 80%.
As for petrol, LRP was available until last year I think. Now you just get two varieties of unleaded. There was a scare campaign a few years back when 10% ethanol blends were introduced and people thought it would damage their cars so it went out of fashion. The problem was the plastic parts in the fuel line could dissolve. Not a problem for my Model T Ford [Linked Image]
Diesel and petrol are about the same price here ~$1.20 per litre with LPG about half that.