Chances are you've never tasted crude oil, and if you had the chance, you'd probably pass 99.9% of the time. Interestingly, however, crude oil tastes sweet when its sulfur concentration is lower than 0.42% per volume. Sulfur in crude oil is an impurity, and gives off the smell of rotten eggs when found as hydrogen sulfide.
Sour crude oil has a sulfur volume higher than 0.50%. The terms "sweet" and "sour" originated from the practice of nineteenth century prospectors who would literally taste or smell the crude to determine its quality.