This is a really good overview of oil refining. I'll add a few things.

1. The light and heavy distinction is covered by a measure called API gravity [1]. The higher the API gravity, the lighter the crude;

2. Refiners mix different crude types depending on what kind of refined products they want to produce;

3. Heavy crude tends to be less valuable although it's essential for some applications. Lighter crude produces generally more valuable products like gasoline, diesel and avgas. But heavy crude goes into construction (eg roads) and fuel for ships (ie bunkers));

4. Most refineries in the US are very old and are very polluting. They don't need to be this way. A new refiner would produce vastly less pollution but they're almost impossible to get permission to build now. One exception is the Southern Rock refinery currently being built in Oklahoma [2], which will be powered by largely renewable energy and produce a lot less emissions than an equivalent older refinery with the same capacity;

5. There are different blends of gasoline that the US produces. The biggest is so-called summer and winter blends. What's the differene? Additives are added to summer blends (in particular) to increase the boiling point so less of the gasoline is in gas form because that produces more smog;

6. California uses their own blends so in 2021-2022 when CA gas went to $8+, it wasn't just "gouging". It doesn't really work that way. CA requires a particular blend that only CA refineries produce so it's simple supply and demand as no new capacity gets added to CA refineries and demand goes up with population growth.

The reason for the CA blend goes back to the 80s and 90s when smog was a much bigger problem. Better vehicle emissions standards since then as well as improvements in the blends the rest of the country uses have largely made the CA blend obsolete so CA is really paying $1+/gallon more for literally no reason; and

7. California doesn't build pipelines so is entirely dependent on seaborne oil imports (~75%) despite the US being a net energy exporter. Last I checked, ~20% of that foreign oil comes through the Strait (from Iraq, mostly) so, interestingly, CA is more vulnerable to the Strait of Hormuz closure than the rest of the country.

I guess I'll add a disclaimer: I'm very much pro-renewables, particular solar. I think solar is the future. But we currently live in a world that has huge demand for oil and no alternatives for many of those uses (eg diesel, plastics, construction, industrial, avgas) so we should at least be smart about how we go forward.

[1]: https://en.wikipedia.org/wiki/API_gravity

[2]: https://www.oklahoman.com/story/news/2023/05/24/5-6-billion-...

How an Oil Refinery Works