WordNet (r) 3.0 (2006):

crude oil
    n 1: a dark oil consisting mainly of hydrocarbons [syn:
         petroleum, crude oil, crude, rock oil, fossil
         oil, oil]

Moby Thesaurus II by Grady Ward, 1.0:

19 Moby Thesaurus words for "crude oil":
   avgas, crude, ethyl, ethyl gas, fossil oil, gas, gasoline,
   high-octane gas, high-test, kerosene, lead-free gas, low-lead gas,
   motor oil, paraffin, petrol, petroleum, premium gas, regular,
   rock oil