Why is crude oil measured in barrels?

Crude estimates

Why is crude oil measured in barrels? 

— From medieval times onwards, all sorts of commodities were measured in barrels for convenience, from wine to eels to whale oil. However, standardisation only arrived in fits and starts. Since Richard III’s time, a barrel of wine was defined as 42 ‘wine gallons’, but this wasn’t the same as 42 gallons of water. When the US oil industry started in the mid 19th century, traders adopted the same measure as was used for selling wine. However, in 1824, Britain had standardised a gallon as 20 per cent larger than a wine gallon, the latter of which was renamed a ‘US gallon’. Hence a barrel of oil is only 35 imperial gallons. Because the volume occupied by a liquid depends on temperature, a barrel of oil is further defined as a quantity of oil which fills a barrel at precisely 15.6˚C and one atmosphere of pressure. Why we can’t measure oil by mass – which wouldn’t be weather-dependent – is somewhat puzzling. 

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