Barrels of oil

The media always report statistics of oil production, reserves etc in “barrels”. But how many people know how big a “barrel” is?* Indeed is it an appropriate unit of measurement to use in the context of world energy policy?

The oil industry used to be dominated by American companies, and as with aviation and computers, American units have largely been adopted as the industry standard.

This might not matter since the only people who trade in oil are industry insiders, and arguably the general public do not need to know how big a “barrel” is. They will understand that if OPEC reduces output by x million barrels per day, that’s a lot of oil, and price rises can therefore be expected. In any case, outside the USA, they will still buy the end product in litres.

Yet although it is not a consumer protection issue, there is a problem. Any departure from the International System of Units should be discouraged, as it results in dual labelling, conversion errors, the need to know two systems when one will suffice – and of course general incomprehension.
More particularly, the “barrel of oil equivalent” is used as a
measure of global energy production and consumption. For this, all energy sources (m3 of gas, tonnes of coal, etc.) are converted by energy content into the equivalent energy available in a barrel of crude oil.

BP produces an annual report of world energy consumption and has just produced this year’s. See
I notice that they are now using the tonne of oil equivalent alongside, or sometimes in place of the barrel. Whilst this is clearly an improvement, it doesn’t really give you what you’re looking for. If you’re talking about world energy consumption, rather than just oil, then surely joules (or gigajoules – GJ) are the unit they should be working with? I can see some logic in using a quantity of oil to measure reserves, and refinery throughput, but if you’re comparing nuclear and gas, for example, what has oil got to do with it? The joule only gets a mention in the conversion tables – 1 tonne oil equivalent ~= 42 GJ.

*A “barrel” is 42 US gallons (equivalent to approximately 159 litres)

3 thoughts on “Barrels of oil”

  1. Why am I (are we) receiving emails of old MV posts? They’re interesting to look back over, but I’m sure there’s a bug in the system somewhere!

    [UKMA Secretary’s Reply]
    No, there is no bug in the system. I recently took over as Secretary of UKMA and got old backups of Robin Paice’s MV articles from Derek Pollard, the previous Secretary. Many were lost from the MV site when they were migrated to a new system.

    I have recently been restoring old lost articles to Metric Views on WordPress using the original categories and publication dates. In my opinion, these articles are a matter of historical interest and contain valuable information about metrication in the UK.

    We shouldn’t lose any articles from the website.


  2. It seems that even the dear old barrel is misrepresented by the Americans. Over hundreds of years, the standard volume for a barrel became 36 imperial gallons, UK stylee. Yes, okay, a wine barrel was slightly shorter than that, whereas barrels useful other liquids other than beer might have been slightly more. But in time almost everybody came to accept that a barrel was 36 gallons, and even the barrel delivered to pubs with the retail beer in was a quarter of a barrel ie nine imperial gallons. Also called a firkin, a half barrel being a kildakin, old shortened words for a fourth-part, and a half-part.

    Then along comes the good old US of A, who pluck 42 of their abbreviated gallons out of the air, which is a good two and a bit gallons short of the British imperial barrel, so there is no sensible correlation there from the outset. Why not go for weight instead, since America seems so fond of measuring aircraft fuel in pounds (whereas the rest of the world uses tonnes and kilograms fuel)? It would make more sense, and at least there would only be the need for one relatively straightforward conversion.

    But oh no, nothing that simple! And why not simply tons of crude oil, as to measure the volume would end up with some pretty mind blowing numbers of litres!

    But the stupidest thing is that crude oil never sees the inside of a barrel, hasn’t done for decades now. The use of US barrels to measure oil production, and to measure the energy needs of the world, is so bizarrely outdated that the Europeans of the 19th century, and much of the rest of the world that wasn’t coloured pink on maps, would fall off their chairs laughing at the absurdity of it all.


  3. Quoting oil by mass rather than volume makes eminent sense, especially if we are concerened about CO2 emissions. Basically, whenever a unit (kg, tonne etc) of hydrocarbon is burnt, it create 3.14 units (approx) of CO2.

    Densities of hydrocarbons vary greatly. Methane and butane are gasses at normal pressure and temperatures while octane (petrol) is much less dense than the heavier hydrocrabons that make up diesel. Thus a litre of diesel will produce far more CO2 than a litre of petrol whereas a kilogram of diesel will produce about the same amount of CO2 as a kilogram of petrol.

    Basically hydrocarbons are made up of a chain of linked carbon atoms. Each carbon atom is attacjed to two hydrogen atoms and the first and last carbon atoms each have another hydrogen atom. Thus one molecule of any hydrocarbon consists of N atoms of carbon and 2N+2 atoms of hydrogen. (The value N determines the type of hydrocarbon – methane, ethane, octane etc). When one molecule of a hydrocarbon is burnt, it will produce N molecules of CO2 and (N+1) molecules of H2O. Carbon has an atomic mass of 12, Oxygen is 16 and hydrogen is 1. Substituting these values we see that if N is 1 (ie for methane), 16 (=12 + 4*1) units of methane will produce 44 (12 + 2*16) units of CO2 (a ratio of 2.75) . For N = 2 (ethane), the ratio become 2.93, for N=3 (propane), the ratio becomes 3.0, for N=4 (butane), the ratio become 3.03, for N=8 (octane), the ratio become 3.08 and so on. As N becomes larger and larger, the value tends to 3.14.

    Liked by 1 person

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