The first point needs some editing. Petroleum does not begin with pentane (C5) : most petroleums will contain all lighter paraffinic molecules ; this is confirmed by the sketch in item 13, where you do see the C1-C4 cut. Part of this gas is separated at the wellsite, being called "associated gas" ; but another part stays in the liquid. This gas is hardly stable with the liquid, and all installations (tanks, ships) allow for degassing.

I was wondering about this. There are clearly gasses mixed in the oil. Even on Figure 6, there is propane and other gasses listed as oil products. I'll see if I can figure out a way to say this.