Dear, i would suggest you not to go for it if u r going to fix it in your car there are lot of forum on pakwheels which says CNG price is going to b 15+ and LPG is going to take over CNG very soon. PSO has started installing LPG units and other things like LPG is better than CNG
so if u do want to go for any other fuel go for LPG but the best is to stick to petrol