Exclusive control of 'easy access to Oil' is overwhelmingly the power in that value chain.

The 'first order' issue is earlier in the process, it's that 'House of Saud' keeps most of the surplus for their family and furthermore use it to do some suppressive things.

The fossil fuel market it is very open, and market oriented. It has obvious geostrategic artifacts (notably the petrodollar, some politicians refusal to build pipelines, military support of interventions, OPEC), but it's generally open season. Nobody controls the flow of spice melange.