Volume conversion

This article is for conversion factors and standards for volumes of petroleum. What might seem like a simple subject is complicated by the fact that we have three domains in which to measure a quantity of petroleum: volume, weight (or mass), and energy content. Because hydrocarbons are always complex chemical mixtures, with a huge variety of molecular weights and physical properties, the conversions are imperfect and difficult to standardize.

To make matters worse, each domain has at least two units of measure to it. And to make things even worse, much of the industry uses non-standard prefix multipliers. If you're a writer, respond to the chaos by defining everything and being crystal clear about units. If you're a reader, always ask for clarification.

Oil volumes
Units encountered include bbl, STB (stock tank barrel to specify a barrel at surface conditions), and m3 or Sm3 (standard metres cubed), most often in Europe outside the UK.

1 barrel of oil = 42 US gallons = 159 litres = 0.159 m3.

So 1 m3 = 6.29 barrels.

In commercial settings, it is common to see the tonne used instead of the barrel. Since oil usually has a specific gravity in the range 0.75–0.95, the tonne is bigger than 1 m3, and usually contains about 6.8–7.6 bbl.

Rates are usually given in barrels per day, which might be written bbl/day, bbl/d, b/d, bpd or bopd (uppercase or lowercase).

Gas volumes
Units encountered include the standard cubic foot, scf or cf (sometimes uppercase), and the standard cubic metre, Sm3. Since the cubic foot is rather small, and since the price of gas is given in $/MMBtu (dollars per million British thermal units), which is almost the same as $/Mcf, it's more usual to see Mcf (for thousand cubic feet), MMcf (for millions), Bcf (billions) and Tcf (trillions).

1 Sm3 = 35.3 scf

1 million scf = 28 300 m3

Energy content
The barrel of oil equivalent or boe (pronounced bee-oh-'ee) is a unit of energy, not volume, though it is used as a pseudo unit of volume, usually to allow the combination of hydrocarbons of different gravities and thermal content, including combining liquid and gaseous hydrocarbons. However, there is no clear standard, and the term is therefore not entirely quantitative. As a result, the conversions are approximate, since volumes (and energy content) vary with composition. 1 boe contains about 6.1 GJ.

1 boe is defined as 5 800 000 Btu by the Inland Revenue Service of the USA.

1 toe (tonne of oil equivalent) is not used in upstream business, but is used in some commercial and downstream settings. It is equal to about 42 GJ, or 6.8 boe.

One standard cubic foot of natural gas yields about 1010–1070 Btu when burned, depending on composition. It follows that 1 boe is about 5420–5740 standard cubic feet of gas. The USGS rounds this number to 6000 cubic feet, or about 170 m3 (as in their petroelum assessments, for example ).