The petrol will attack the asphalt, dissolving the tar out of it. About the best you can do I would think is to flush the area with water to try and dilute it / wash it away. Don't use a water blaster as you'll just blast away the now soft/loose asphalt.
If you ever get an oil leak on asphalt just ignore that - the oil seeps in and disappears over time without hurting the surface. It takes a month or two. I have an asphalt drive myself.
The views expressed above may not match yours - But that's the reason my Dad went to war - wasn't it?
Life's journey is not to arrive at the grave safely in a well preserved body, .... but rather to skid in sideways, totally worn out,... shouting "man, what a ride"!!!
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