Mike,
>> By geological dating, right?
Sort of. The oil is dated by seeing how much it has aged from a presumed
original composition. Crudes age in variuos ways, but usually become heavier
(thicker) with age. This coupled with the idea that each source rock produces
a unique product allows you to date the oil. Souce rocks in the Gulf are dated
by fossil assemblage. Crude oils differ from reservoir to reservoir, and it is
possible to analyze a crude oil (not refined product) and determine it's
source, or if it is a blend from several reservoirs. Tanker spills can be
identified by the signature of the crude.
Jim