What is oil?

7 min readOct 11, 2021
Image from a long time ago, when oil used gush into the air from shallow wells. Signal Hill, California 1923. Image source

This article was really long due. I’m writing a lot about oil on this blog and since it is so important to this civilization, I wanted to highlight some basic (plus some “fun”) facts about it. I’m sure you have a picture in your mind what crude oil (petroleum) is — chances are though, that if you are not a petroleum-geologist this image is wrong. I myself used to have a rather simplistic image about the “black gold” too, until I spent the last couple of years trying to understand what it really is. In this post I make an attempt at trying to explain this rather complex topic in concise way. (If you do happen to be an expert please feel to correct me if I made a mistake.)

Buckle up!

First, let’s start by stating what oil is not. First, it’s neither the blood of Earth originating from the rocks themselves (not in any meaningful quantities at least), nor the blood of dinosaurs. Second, our planet is not like a giant liquor bonbon filled with petroleum either.

Third: oil is not a modern invention. Homo sapiens first met crude oil accumulated in pits where all one needed to obtain petroleum was a bucket. The substance was already in use 4000 years ago during the construction of the walls and towers of Babylon (in the form of asphalt), and later for lighting and medical purposes by the upper classes. By 347 CE, oil was “produced” from bamboo-drilled wells in China as well. Persian chemists knew how to refine it into various products more than a thousand years ago.

Widespread, large scale extraction and use was started in the USA during the second half of the 19th century to provide a replacement for whale oil. (Whales were hunted to near extinction to obtain their oil used in lamps for lighting.) Gasoline (petrol in the UK) was a waste back then (an unwanted side product of distillation process) and was released into nearby rivers — untreated... Carl Benz hit two birds with one stone when he invented the petrol-engine: he helped to get rid of an enormous environmental problem, and found a much more efficient (cheaper, lighter, faster) power source than steam engines. With this invention and the discovery of large quantities of oil in Texas, he and Rudolf Diesel has opened the door to a much bigger problem, but that’s a different story.

So what is oil then?

Well, it’s certainly the lifeblood of this civilization. It is also of biological origin: it has started to form hundreds of millions of years ago when dead plankton and other plant matter sank to the bottom of a lake or the sea. If conditions were right (i.e. low oxygen levels, and sediment accumulating on the top of this underwater “compost heap”), then a very slow process began. It involved heat from below and pressure from the rocks (formed from the sediment) above. If the dead matter sank too deep into Earth’s crust and got too much heat, it then turned into gas. If it wasn’t deep enough long enough, then oil failed to form, or it oozed out and was washed away quickly.

As a result oil and gas could be found in pockets of various sizes. Large pockets are very rare, while small pockets are numerous (FYI: they follow a power-law distribution). You need to drill far fewer wells to tap large fields, which will yield oil for decades, while you have to play “hit or miss” with every little pocket by drilling yet another hole… and expect them to run out of oil much sooner than larger wells. Not a winning proposition if you had already tapped your large fields and all you have is small bubbles here and there.

Petroleum’s formation process together with the distribution of oil fields, of course, is well known to geologists for a long time now. Since Earth is a sphere with a finite surface area, and with a finite number of possible locations, I do not expect large discoveries in the future. (Fun fact: the linked FT article gave a forecast to our problems today based on this process four and a half years ago. Exploration budgets were cut worldwide due to their low returns in discoveries: since all the major fields were found already, adding small pockets here and there didn’t really help oil companies.)

What’s your favorite blend?

Octane — a typical hydrocarbon molecule found in petroleum. Black balls represent carbon atoms, whites are hydrogen. Imagine how many different combinations you can make from these two simple components: from a single carbon atom and 4 hydrogen (CH4 — or methane) to ultra long molecules almost endless in length.

Beside it’s distribution petroleum has another very important aspect with regards to its usability. Crude oil comes in many tastes and flavors: there is sweet, sour, light, heavy, extra heavy, shale (kerogen), bitumen from oil sands etc. Oil is not a single uniform substance: each type has different properties and different extraction costs.

The primary distinction lies in the length of hydrocarbon chains crude oil consists of — and not all blends are equally useful for us. It is very important to find oil with the right composition: it must not be too heavy (with too many long molecules), nor too light (with too many short molecules). The “ideal” crude, like Brent has a mix of long, short and medium length hydrocarbon chains. When distilled in a refinery it yields a number of different products from asphalt to make roads, heavy oils for lubrication, diesel to power trucks, kerosene for aircraft engines, and light stuff like naphtha (the raw material for plastics) and gasoline for our cars.

Petroleum primary consisting of long hydrocarbon chains is considered heavy, extra heavy or bitumen (increasing in thickness in this order). This stuff barely pours under its own weight and have to be heated to crack long molecules, and/or diluted with lighter oils in order to forward it via pipelines or ships. This means higher extraction costs as well: you have to boil water and inject the steam into the well to heat and force the substance upwards through a tight hole. Then you have to import (buy) lighter oils to dilute it, finally selling the mixture at a lower price than “normal” crude. Is it any wonder Venezuela almost went broke trying to extract it’s wast heavy oil reserves in the Orinoco belt? Hardly. The same is true with Canadian tar sands: requiring very high energy inputs to coke it… hence making it the most polluting and expensive form of oil extraction — but hey, at least corruption levels are bit lower up north!

On the other end of the thickness scale one finds shale oil (tight oil to be precise). This material is so light (it’s almost like pure gasoline) that on it’s own it is largely worthless to the economy. OK, you get cheap gas out of it, but what about diesel to power trucks and ships, or heavy oils for lubricants? Light tight oil is only viable in the US because Canadians have bitumen from tar sands. (The former is used to dilute the later — even though they do not mix perfectly and tend to block pipelines from time to time.) It’s no wonder that refineries don’t like to work with them too much: they’re gunky and costly to break down into products, which can be sold at regular prices only.

Tight oil has another major disadvantage: cost of extraction. One has to drill ten thousand feet deep, then another ten thousand feet sideways (what a technical feat!), explode holes into the well, then inject a toxic mixture at an enormous pressure to crack the source rock itself. After removing the toxic water, tons of sand needs to be poured down the hole to keep the rocks collapsing on each other. None of this is required in case of a normal well — meaning extra cost and energy… Not to mention road damage caused by trucks delivering many thousand loads of sand and water to the fracking site. If this weren’t enough, all this fuss is performed for a well, “producing” oil for a couple of years only (vs decades in case of a regular well), then the whole process needs to be repeated at another location.

What comes out of this?

As you have seen above petroleum, is not a uniform substance. It varies greatly both in distribution and quality. Unfortunately we have harvested the best quality, easy to obtain stuff first and now we are increasingly forced to use unconventional (low quality, hard to tap) resources. Even though it seems that we have plenty of oil left, what remains is becoming ever less economic to find, extract and process… forcing us to leave most of it in the ground. On one hand this is very good news: we will most probably never reach the horror scenarios of climate change. On the other hand, lacking a suitable alternative energy source, our current problem with oil supply, which have it’s roots 10–15 years back in time, might be a sign of this civilization reaching its limits.

Until next time,





A critic of modern times - offering ideas for honest contemplation. Also on Substack: https://thehonestsorcerer.substack.com/