The Collaborative International Dictionary of English v.0.48:

Petrol \Pe*trol"\ (p[-e]*tr[=o]l), n.
   1. Petroleum. [Archaic and R.]
      [1913 Webster]

   2. (p[e^]"tr[add]l"), Same as gasoline; -- British usage.
      [British]
      [PJC]

WordNet (r) 3.0 (2006):

petrol
    n 1: a volatile flammable mixture of hydrocarbons (hexane and
         heptane and octane etc.) derived from petroleum; used
         mainly as a fuel in internal-combustion engines [syn:
         gasoline, gasolene, gas, petrol]