There is another American/British thing: measuring oil production in barrels, that is by volume.
1 US bbl = 42 gallons. This dates back to the early American oil industry where oil was stored in 42 gallon wooden barrels and was purchased by the barrel. To this day US petroleum engineers refer to the measurement of oil and gas in volumetric terms.
Depending on the application hydrocarbons and gas are measured in terms of volume, weight and/or thermal energy. Broken down into the following main groupings, these distinctions make sense:
- VOLUME: Engineers (particularly in the upstream) must make volumetric determinations. All drilling, completions and production considerations are tied to volume occupied by the fluid in question - be it oil, gas or water. Temperature is essentially constant within the reservoir and for the majority of crude the differential between the reservoir and the surface is not hugely consequential. The math is more "involved" for natural gas and gas condensates are complicated.
- MASS: Oil Tankers are less concerned with volumetric capacity. There's a huge difference betweeen equal volumes of heavy Venezuelan and premium Brent crude where an oil tanker's freeboard is considered.
- ENERGY: The downstream energy industry is concerned about the thermal energy content of products.
Europe, the former USSR in particular, measure crude oil by it's weight in metric tonnes per day. The conversion from Tonnes to barrels is roughly 7.33 barrels = 1 Tonne. This is not unitary blasphemy as the 7.33 barrel conversation is based on a worldwide average oil gravity.
So yes, volumetric measurements make sense for the upstream, but for literally any other consideration - mass is the way to go.
Why is this a thing?!?!