Considering petrol is oil based, I wouldn't be using it on my brake pads.
Give everything a good clean with metho or isopropyl alcohol, and let the pads soak in it for a good while. Then you can burn it off if you're a pyro or just let them dry out and they should be alright. You may need to get some sandpaper onto the braking surfaces of the pads/rotors just lightly to roughen them up a bit, too.
Otherwise, buy new pads, clean everything else well.