Conversion Factors

Oil markets run on three different measuring sticks at once. Physical cargoes are weighed in metric tonnes. Futures contracts are priced in dollars per barrel. Refinery margins and retail prices are quoted in cents per gallon. Natural gas and LNG are priced in dollars per million British thermal units. A single trade might specify a cargo in tonnes, a price in dollars per barrel, a margin in cents per gallon, and a heat-rate assumption in Btu per cubic foot, all on the same ticket. Getting the conversions right is not optional. It is the baseline skill of anyone moving, pricing, or hedging hydrocarbons.

There are two reasons the arithmetic is less mechanical than it looks. First, volume and mass are not interchangeable for oil. Because density varies by crude grade, the barrel-to-tonne factor is not a single constant. Light sweet WTI runs roughly 7.52 barrels per metric tonne. Heavy Mexican Maya is closer to 6.6 barrels per metric tonne. The same 1 million-barrel cargo can weigh 133,000 tonnes or 151,000 tonnes depending on what is loaded. Second, energy content also varies. A barrel of gasoline holds roughly 5.1 million Btu. A barrel of residual fuel oil holds roughly 6.3 million Btu. The concept of a “barrel of oil equivalent” papers over these differences with a convention (6 MCF of natural gas per BOE) that is neither a thermal parity nor a price parity.

This appendix collects the physical constants, the rounded industry-standard conversion factors, the distinction between high and low heating values, and a few worked examples readers actually run into. Chapter 2 (Crude Oil Assay) covers the underlying concept of API gravity. Chapter 14 (Reserves) covers barrels of oil equivalent for reserve reporting. Use this appendix as a reference card when the arithmetic matters.

Density, API gravity, and why the barrel-to-tonne factor moves

Density is mass per unit volume. For petroleum liquids it is conventionally measured relative to water at a standard temperature, most often 60°F in the US and 15°C in the rest of the world. The ratio is called specific gravity. A fluid lighter than water has a specific gravity below 1. Water itself has a specific gravity of 1 and a density of 1,000 kg/m³.

API gravity is a rescaling of specific gravity chosen by the American Petroleum Institute so that a more commercially useful crude gets a higher number. The formula is API° = (141.5 / specific gravity) − 131.5. Water comes out at 10° API. Light sweet WTI runs roughly 40° API. Heavy Mexican Maya runs roughly 21° API. The higher the API number, the lighter the crude, the more barrels per tonne, and typically the higher the value of the yield barrel at the refinery. Table A2-1 below shows the physical density and energy values for a representative set of fuels from methane at the light end to residual fuel oil at the heavy end. These are physical constants, not market prices, and they do not change with the year.

Table A2-1: Approximate Density and Energy Values

Energy values in this table are low (net) heating values. See the discussion of high versus low heating values below. Source: Oil 101, Morgan Downey, first edition Table A2-1.

Standard oil-industry conversion factors

Table A2-1 gives the precise physics. In day-to-day trading you rarely need that many significant figures. Traders, schedulers, and analysts run a smaller set of rounded factors in their heads. Table A2-2 collects the ones that actually get used. These are the numbers that belong on a business card.

Table A2-2: Standard Oil Industry Unit Conversions

High heating value versus low heating value

When a hydrocarbon burns, one of the combustion products is water vapor. How that water vapor is counted is the difference between the two ways of quoting energy content.

The high heating value, also called gross calorific value or HHV, includes the latent heat of vaporization of the water produced in combustion. You get the high heating value if you condense the water vapor back to liquid and capture that heat. The low heating value, also called net calorific value or LHV, excludes that latent heat. You get the low heating value if the water vapor escapes out of the exhaust as vapor and you never recover the heat it is carrying.

Almost every engine that burns a liquid fuel, and almost every older gas-fired industrial burner, exhausts the water as vapor. So low heating value is what gets quoted for transport fuels and for most industrial combustion applications. The energy values shown in Table A2-1 are low heating values.

High heating value matters for modern condensing natural gas power plants and condensing domestic boilers, which are designed to cool the exhaust below the dew point of water and recover the latent heat. A condensing combined-cycle gas turbine running on pipeline-quality natural gas can get efficiency a few percentage points higher on an HHV basis than a non-condensing unit of similar design. Europe tends to quote boiler efficiency on a net (LHV) basis, which can make a European 90 percent efficient boiler equivalent in real terms to a US 81 percent efficient boiler. Always check which basis a quoted efficiency is on.

Barrel of oil equivalent accounting

Reserve reports and production statistics often aggregate liquids and gas into a single number called barrels of oil equivalent, or BOE. The US SEC rules use a fixed conversion of 6,000 cubic feet of natural gas to 1 BOE. This is a regulatory convention, not physics. The thermal parity of gas to oil (matching Btu to Btu, at roughly 5.8 million Btu per barrel of crude and 1.036 million Btu per MCF of gas) comes out closer to 5.65 MCF per BOE. And the price parity moves all over the map. When oil trades at 80 dollars per barrel and Henry Hub gas trades at 3 dollars per MMBtu, the economic ratio is about 4.6 MMBtu of gas per barrel, or roughly 25 MCF per BOE. Aggregating at 6:1 overstates the cash value of gas-weighted reserves when gas is cheap relative to oil, which is why you will occasionally see operators report “oil and liquids production” separately from the headline BOE number. Chapter 14 (Reserves) covers how this affects reserve replacement ratios. For this appendix the takeaway is: BOE is a unit of account, not a unit of energy, and not a unit of cash.

Worked examples

A VLCC loads 2 million barrels of Arabian Light crude for a trip to Asia. How many metric tonnes? Arabian Light runs roughly 0.137 metric tonnes per barrel. 2,000,000 times 0.137 equals 274,000 metric tonnes. That is a standard VLCC parcel. A voyage charter quoted in Worldscale against a 274,000-tonne reference cargo is priced against exactly this kind of math.

A refiner buys a 50,000 metric-tonne cargo of vacuum gasoil at Rotterdam and wants to hedge it against ICE gasoil futures, which are denominated in tonnes, or against Brent futures, which are denominated in barrels. Typical VGO runs about 1.14 barrels per tonne, so 50,000 tonnes equals roughly 57,000 barrels of Brent futures equivalent. For a one-for-one hedge at 1,000 barrels per contract the refiner needs 57 Brent futures. The basis risk of using Brent against VGO is a separate question from the tonne-to-barrel conversion.

A refiner reports a 3-2-1 crack spread of 24 dollars per barrel on its earnings call. What is that in cents per gallon on the product side? Dividing 24 by 42 gives 57.1 cents per gallon, because each barrel of crude yields 42 gallons of product in the crack-spread convention. The same math runs the other way: a retail gasoline margin of 30 cents per gallon is worth 30 times 42, or 12.60 dollars per barrel of gross margin at the pump.

A gas producer is hedging 100,000 MMBtu per day of Henry Hub exposure against NYMEX Henry Hub futures. Each futures contract is 10,000 MMBtu. The producer needs ten contracts per day of production. On an annual basis, 100,000 MMBtu per day times 365 days is 36.5 million MMBtu, which is 3,650 contract-months of exposure. If the producer also wants to express that volume as a BOE-equivalent at the 6:1 convention, 100,000 MMBtu per day divided by 5.8 MMBtu per barrel of oil equivalent is roughly 17,240 BOE per day. At the SEC 6:1 convention on a volumetric basis, the same production would round to 16,080 BOE per day. Both conventions are in use, which is why reserve footnotes usually specify the basis.

A caution on precision

The factors in Table A2-2 are rounded to the level you can run in your head or on the back of a fuel ticket. For contract settlement on a specific cargo, the only correct density is the one on the cargo assay certificate. For tax, customs, and SEC reserve filings, the applicable regulator specifies the exact conversion factor to use. Do not mix the two. A trader who uses the head-math numbers from Table A2-2 to settle a multi-million-dollar cargo is leaving money on the table or overpaying. A reserve auditor who pulls grade-specific density out of an assay instead of using the filing-mandated factor is creating a restatement risk. Use the right tool for the job.