Anotherwords, re API gravity, we are looking for a field full of octane molecules if I remember my organic chemistry lessons (mostly self taught). If the gas at the pump was all octane it would be 100, it's the benchmark molecule for automotive fuels. In reality you are pumping a combination of other molecules, some 7s, some 6, some 5s, and  of course all the environmental additives, but mostly 8s, some octanes, some octenes, which has to do with single bonds or double bonds between the carbon molecules.

10 carbon atom molecules is kerosene as I recall and that is pretty close to jet fuel. You get up past 40-45 atoms then you are in the tars and bitumen, the bunker oil, some of which you can actually shovel. Geologically after that point you are looking at solids, eventually looking for seams of coal. It's all the same stuff. At the other end are the volatile gases, ethane, pentane, butane and everyone's favorite propane, which all evacuate out of the very top of the cracking tower.

Hope this helps. Oiljob ....  (like I said, I never took that chemistry class, I was a geology/law student).