I can't answer your question directly but, I used to buy asphalt from Ashland who later merged with Marathon and at one time made Valvoline products. In simple terms, asphalt is the gunk that is left over after a refinery takes all the light ends (gasoline, oils, lubes) out of the crude. We were always very interested in the quality of our asphalt because we modified it into a high performance polymerized compound that was guaranteed for elasticity at extreme temperatures. Anyway, it forced me to learn a thing or two about the refinery business.
Ashland bought crude from all over the world every day and would blend several products to hit a predetermined specification encompassing several parameters. To my knowledge, they never refined a single crude, they always blended. It is my understanding that most large refiners operate this way simply to safeguard supply. However, there are smaller specialty refiners who pull a single crude from a single field and pride themselves on the consistency of their product. I suspect the major motor oil producers pull from refineries that blend simply because of the volumes involved. There could be smaller boutique oil producers that use one of these single field refiners but I don't know who they might be.
