What types of crude oil exist?

When buying and selling unrefined oil on the world market (or any other raw material, for that matter, from iron ore to cotton to sugar) there have to be ways to grade the goods so that they can be adequately compared to “similar goods” from other suppliers.

I don’t pretend to know all of the various grades of unrefined fuel oils, but Wikipedia does a pretty good job of explaining what this means.

When it comes to coal as fuel, there is no simple way of grading one coal against another. Coals vary so widely from place to place in the world that each coal field has a “proximate analysis” performed to rate various aspects of the coal so that it can be rated as a boiler fuel. Those measures include moisture content, ash content (how much will have to be scraped out of the boiler bottom and disposed of after burning), sulfur content (so we can plan the air quality control system SO2 scrubbers), “high heating value”, “grindability” and other physical characteristics that relate to how well it burns, how much of it burns, what aspects require “handling” in the boiler, and how much heat it gives off when it does burn). Many of those features also pertain to oil, of course – maybe not “grindability” – but I think the range of petroleum variations is generally narrower than it is for coal.