Engine driver? (9)
'engine driver?' is the definition.
(the fuel that drives the engine)
This is all the clue.
(Other definitions for petrol that I've seen before include "Mineral oil refined as fuel" , "Liquid fuel" , "Common motor fuel" , "Gasoline" , "Fuel for road vehicles" .)
(Other definitions for petroleum that I've seen before include "Fuel oil" , "It helps in getting things moving" , "Source of fuel" , "Fossil fuel" , "Oil well product" .)