This will be a good topic for a blog.
Oil and Gas are minerals. A diamond is a mineral. Just as diamonds have varying grades, so do oil and gas. Gas is graded on impurities and the heating content. 1 mmbtu should be equal to 1mcf at standard pressure and temperature. It could have less heating content because of impurities – such as h2s or water vapor. It could have a higher heating content based on the richness of the hydrocarbons because of the quantity of condensate.
Oil, likewise has its impurities, such as paraffin and hydrogen sulfide. Oil is generally sold based on various benchmarks. In Texas, it is West Texas Intermediate. There are also gravity adjustments to price, based on how heavy or light it the product is. Heavy oils are more suitable for refining to lubes, heating oils, etc (Venezuela and Canada are famous for their heavy crudes). Lighter oils are more suitable to refining into gasoline and jet fuels. As a matter of fact, there is sometimes a natural refining of hydrocarbons in the reservoir itself, so that the product produced is a natural gasoline that you could run in your truck.
Can one county have more than one grade of crude oil. Of course. It really depends on the depositional characteristics and property of the source rock. I want to say that Live Oak County has both sweet and sour gas, depending on the formation produced from, for example.