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 www.bp.com/statisticalreview
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)
June 20th, 2007 at 04:17
I know the Chinese don’t buy their oil in barrels. They buy it by the tonne. This way they get a consistent amount. A barrel may be 159 L, but that depends on the temperature. When it is cold, the density of oil is greater, when it is hot, it is lesser.
When you buy gasoline in the winter months you get more per litre and in the summer it is the opposite. Since the mass of the fuel is independent of temperature, it is best to buy and sell by mass, that is the kilogram or megagram (tonne).
June 20th, 2007 at 11:32
Energy is a complex subject. There are plenty of natural conversion constants to deal with - densities; energy content of a fuel; efficiency of power stations etc. The whole business is made enormously more complex by introducing a profussion of units with their own conversion factors - weight in short, long and metric tons; volume in US gallons, barrels, cubic metres all at different standard temperatures; energy in MWh, barrels of oil equivalent, tonnes of oil equivalent, therms, BTUs, KCalories etc.
Energy is such an important issue in the 21st century, and it’s only going to get more important. We desparately need to simplify things by using a single, related set of units - namely SI - kg for weight; cubic metres (= 1000 litres) for volume and joules for energy.
June 22nd, 2007 at 03:44
The use of a plethora of units to measure the same thing is just part of the age old trick of making it as difficult as possible to compare.
Air conditioners are usually rated in “BTUs”, yet the power they consume is in kilowatts. Recently the air conditioning industry came up with a new unit to compare the efficiency of the air conditions. It is called EER. It is suppose to be a measure of how many BTUs one gets for kilowatt of electrical power used.
If the cooling capacity was in kilowatts as it should be then there would be no need for EER. One would simply divide the cooling capacity into power consumed to know how efficient one’s air conditioner is.
But why make it easy? Just keep coming up with more and more useless units to keep the population in a permanent muddle.
October 17th, 2007 at 06:07
The use of barrels stems back to the days before the carriage of oil in bulk, when oil like wine was carried in large wooden barrels, hence the name, and a buyer would purchase a number of barrels of oil, or a ship would carry x number of barrels of oil. The barrels were of a standard size and therefore a buyer would know how much oil they were purchasing. I agree that there is no obvious reason to continue to use the standard today, but it is no different to say a bolt of silk, a troy ounce of silver or a ream of paper. I suppose tradition will out in the end. As you say the oil industry knows what it is all about.
June 18th, 2008 at 21:35
The origins of the 42-gallon oil barrel are obscure, but some historical documents indicate that around 1866 early oil producers in Pennsylvania came to the conclusion that shipping oil in a variety of different containers was causing buyer distrust.
They decided they needed a standard unit of measure to convince buyers that they were getting a fair volume for their money. They agreed to base this measure on the more-or-less standard 40-gallon whiskey barrel, but added an additional two gallons to ensure that any measurement errors would always be in the buyer’s favor as an additional way of assuring buyer confidence (The same principle as behind the baker’s dozen and some other long units of measure.) By 1872 the standard oil barrel was firmly established as 42 US gallons