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]

Moby Thesaurus II by Grady Ward, 1.0:

27 Moby Thesaurus words for "petrol":
   avgas, benzine, coal oil, crude, crude oil, electricity, ethyl,
   ethyl gas, fossil oil, gas, gasoline, high-octane gas, high-test,
   illuminant, illuminating gas, kerosene, lead-free gas,
   light source, low-lead gas, luminant, motor oil, oil, paraffin,
   petroleum, premium gas, regular, rock oil