When transporting loads of crude oil, it’s helpful to be able to calculate the weight of your cargo in order to comply with weight regulations. Since a gallon is a measure of volume and not weight, how much does a gallon of crude oil weigh?
How much does a gallon of oil weigh? The weight of crude oil ranges from 6.5 lbs/US gal to 8.5 lbs/US gal as crude oil ranges in grade from light to heavy. Since the weight of oil is also affected by changes in temperature, the petroleum industry uses measurements that account for those changes.
How to Calculate the Weight of a Gallon of Oil
In order to convert volume in gallons into weight in pounds, you will need to know the density of the liquid as well as the temperature. The measures established for this purpose are specific gravity and API gravity.
The United States Bureau of Standards (changed to the National Institute of Standards in 1988) adopted the Baumé Scale in 1916 to establish the specific gravity of liquids (source).
Specific gravity measures the density of a liquid in relation to a standard liquid like water at a specific temperature. Specific gravity is found by dividing the mass of a substance by its volume and then dividing the result by the density of water at the same temperature (source).
If you know the specific gravity of a liquid, you can calculate its weight in pounds by multiplying it by the density of water in pounds per US gallon (lbs/US gal) at a specific temperature.
The American oil industry uses 60°F (15.6°C) as a base temperature for measurement, and all numbers in this article are based on this standard. The density of water at that temperature is 8.3369 lbs/US gal. Since Canada uses the metric system, they use 15°C (59°F) as a base temperature, and that would be 8.3379 lbs/US gal (source).
The petroleum industry has established a measure known as API gravity to measure the density of petroleum liquids. API stands for the American Petroleum Institute (API) which established API gravity in 1921 in conjunction with the US Bureau of Standards.
API gravity is useful as a measure of value since the higher the API gravity of the oil, the lower its density, and lower density fuels fetch higher prices. To find API gravity, you have to divide 141.5 by the specific gravity of the oil and then subtract 131.5 (source).
Grades of Crude Oil
The basic grades of crude oil are light, medium, and heavy, with different countries and organizations having different standards. The weight of a gallon of light, medium, or heavy crude will differ from the next grade by one quarter to half a pound per gallon depending on the standard used.
Light Crude Oil
Light crude oil sells at a high price because oil refineries can produce more diesel fuel and gasoline from it. Light crude oil also has a very low viscosity and density, flowing freely at room temperature. Light crude oil has shorter hydrocarbon chains than heavier oils.
Light crude oil has a high API gravity and low specific gravity. The majority of crude oil produced in America is light crude oil, although crude oil produced in California is significantly heavier.
The Threshold for Light Crude
The threshold between light crude oil and medium crude oil varies considerably. For example, the US Energy Information Center defines light crude oil as over 40.1° API (source), while the Louisiana Department of Natural Resources defines it as over 31.1° API (source).
The New York Mercantile Exchange (NYMEX) bases the threshold of API gravity for light crude used domestically on West Texas Intermediate (WTI) crude which ranges between 37°API and 42° API (specific gravity of 0.8398 to 0.8156) (source). However, NYMEX lists the API gravity range of light crude oil for export as between 32 ° API and 42° API (specific gravity of 0.8654 to 0.8156).
Since crude oil produced in the United States is much lighter than that produced in either Mexico or Canada, both Canada and Mexico have lower API standards for what qualifies at light crude oil.
The government of Alberta defines it as 35 API, while the National Energy Board of Canada determined that light crude oil can have an API as low as 30.1° (source). Pemex, a state-owned Mexican oil company, defines the limits of light crude oil between 27° and 38° API (source).
Going by the export NYMEX standard, the weight range between 32 and 42 API is 7.215 to 6.8 lbs/US gal or an average of about 7 lbs/US gal. Domestic light crude would then be 7.001 to 6.8 lbs/US gal for an average of 6.9 lbs/US gal.
If we go by the minimum standard of the Louisiana DNR, which is closer to international standards, of 31.1 API, that gives us a minimum weight for light crude oil of 7.255 lbs/US gal.
Extra Light Crude
Crude oil with especially high API gravity between 42 and 50 (6.8 to 6.5 lbs/US gal) is sometimes referred to as super light or extra light (source). One example of extra light crude at 48° API, or specific gravity of 0.79, would weigh 6.59 lbs/US gal (source).
Light benchmark crude oils include North American West Texas Intermediate (39.6°API) and North Sea Brent Crude (38.06°API) with respective weights of about 6.895 and 6.957 lbs/US gal.
Minas crude or Sumatra light crude has an API of 35, OPEC Reference Basket has an average API of 32.7, Bonny Light has an API of 32.9, and Isthmus-34 Light has an API of 33.74. Tapis, from Malaysia, is extra light crude with API gravity of 45.2 (source).
The Dubai Crude, produced by the United Arab Emirates, has an API of 31, which makes it medium crude by American standards. It has a weight of 7.259 lbs/US gal.
Medium Crude Oil
The higher standards of the US Energy Information Center define medium crude oil as having API gravity between 40 and 30. According to the Louisiana Department of Natural Resources, Medium Crude Oil has API gravity between 31.1 and 22.3 (source).
Mars blend crude, which is extracted off the coast of Louisiana, has an API gravity of 28 and a weight of 7.396 lbs/US gal. Mars blend crude is one of the four key benchmarks for US crude including lighter blends like Light Louisiana Sweet, WTI Houston, and WTI Midland (source).
Canadian standards for the maximum threshold range from about 35 to 30 API, while the minimum threshold ranges from 25 to 18 API. Pemex of Mexico defines it as under 27 API.
Going by the often-cited Louisiana DNR standards, we get a weight range for medium crude of 7.255 to 7.54 lbs/US gal.
Heavy Crude Oil
Heavy crude oil is highly viscous and dense with a low API gravity and high specific gravity. The hydrocarbon chains of heavy crude oil are longer than other crudes, and they tend to have more contaminants like sulfur (source).
Heavy crude oils command lower prices on the world market because they require more processing while producing lower quantities of gasoline, diesel, and other products.
The National Energy Board of Canada defines heavy crude oil as anything lower than 25 API or specific gravity of 0.904 (source). However, other standards place heavy crude oil somewhere around 22.3 to 20 API or specific gravity of 0.92 to 0.934 at the most. This translates to 7.537, 7.67, and 7.787 lbs per gallon respectively.
California heavy crude oil weighs about 7.63 lbs/US gal, while Mexican heavy crude oil weighs about 8.11 lbs/US gal (source). West Canadian Select has an API gravity of 21, which converts to 7.736 lbs/US gal.
Extra Heavy Crude
Extra heavy crude oils have an API less than 10 or a specific gravity of 1, which is equal to the density of water. At 60°F, a heavy crude oil with an API of 10 will weigh around 8.3369 lbs per gallon. Anything with an API lower than that will sink in water (source).
Origins of the 42-Gallon Barrel
The 42-gallon barrel is based on the English tierce. The tierce was used as a measure of volume for wine since at least the reign of King Richard III of England (1482-1485), and it became a standard for guilds of professional coopers. The tradition continued in the United States, and they were common in the 19th century (source).
When the first commercial oil well was sunk in the United States in 1859, the extractors needed large quantities of high-volume barrels and casks. They gathered whatever barrels they could, which included 40-gallon whiskey barrels and 42-gallon tierces normally used for wine, fish, turpentine, bear, or molasses.
By 1866, Pennsylvania oil producers recognized the need for a standard volume, and they settled on the 42-gallon barrel. In 1872, it became the official standard of the Petroleum Producers Association.
In 1902, John D. Rockefeller’s Standard Oil Company introduced a steel oil barrel that held 42 gallons to replace the older wooden barrels. These early steel barrels were riveted together and still had a tendency to leak.
How Much Does a Barrel of Oil Weigh?
While the physical 42-gallon barrel is no longer in standard use, the 42-gallon barrel is still used as a measure of volume in the American oil industry. Prices on the American Stock Exchange are still reported in barrels as some variant of the abbreviation bbl. A barrel of oil held 42 US gallons, 35 Imperial gallons, or 159 liters.
A “barrel” of West Texas Intermediate weighs about 289.59 lbs, while a barrel of Brent Crude weighs 292.19 lbs, and a barrel of Dubai Crude weighs 304.88 lbs. A barrel of medium crude will weigh somewhere between 304.71 lbs to 316.68 lbs based on the Louisiana DNR standard.
A barrel of heavy crude oil will weigh over 322.14 lbs, and West Canadian Select will weigh about 324.9 lbs. Extra heavy crude will weigh over 350 lbs per barrel.
The 42-gallon barrel measurement is largely limited to the oil industry, and other industries use a different sized barrel. For example, a wine barrel holds 31.5 US gallons, 26.2 Imperial gallons, or 119.2 liters.
The Adoption of the 55-Gallon Steel Drum
The 55-gallon steel drum was designed by Henry Wehrhahn based on the ideas of his employer, a famous female journalist turned business owner, Elizabeth Sherman (1867-1922), known by her pen name, Nelly Bly (source).
Bly was the widow of Robert Seaman who died in 1904, and she became president of his Iron Clad Manufacturing Company of Brooklyn, New York. Wehrhahan filed for the two patents that were the basis of the 55-gallon steel drum which were then acquired by Nelly Bly.
The subsidiary American Steel Barrel Company was able to produce about 1,000 of these 55-gallon drums a day. However, the company fell into legal trouble by 1911 and was bankrupt by 1912. After serving a brief jail sentence for refusing to turn over certain records to her creditors, Nelly Bly returned to journalism (source).
The 55-gallon drum really came into its own during World War II, where they were critical for transporting fuel oils and other chemicals necessary to the war efforts of Allied and Axis forces alike. It was during this war that militaries established the specifications and dimensions of the 55-gallon drums used today (source).
By the 1950s, companies were phasing out the physical 42-gallon barrels in the oil industry while retaining them as a unit of measurement.
How Much Does a 55-Gallon Drum of Oil Weigh?
The drum is measured in 55 US gallons, which is the equivalent of 45.8 Imperial gallons and 208 liters. The 55-gallon drum remains the standard for shipping large amounts of oil, water, foodstuffs, and chemical waste.
When calculating the weight of a cargo of oil drums, the weight of the drum itself also has to be factored in. 55-gallon drums are now made of steel, plastic, and even paperboard (also called fiber drums). A steel drum will weigh about 40 lbs, a plastic one around 20 lbs, and a fiber drum about 17 lbs.
The oil contained in a 55-gallon drum of West Texas Intermediate will weigh about 379.23 lbs, Brent Crude 382.64 lbs, and Dubai Crude 399.25 lbs. When we add the weight of the steel drum, we get 419.23 lbs, 422.64 lbs, and 439.25 lbs.
As for medium crude, the weight of the oil in a 55-gallon drum will be somewhere between 399 lbs and 414.7 lbs based on the Louisiana DNR standard. Including the drum, that’s between 439 and 454.7 lbs per drum.
Heavy crude oil will weigh over 421.85 lbs, and West Canadian Select will weigh about 425.46 lbs. Meanwhile, extra heavy crude will weigh over 458 lbs. 55-gallon drums of each will weigh about 461.85 lbs, 465.46 lbs, and 490 lbs.
The Age of Supertankers
Large tankers like the US T-3 oil tanker were used during World War II that could carry up to 200,000 barrels. However, the closing of the Suez Canal in 1956 led to the development of the supertanker. Instead of holding actual physical barrels or drums, oil tankers carry oil in a series of tanks.
A supertanker has a deadweight capacity of over 75,000 tons. The first of the supertankers, the S.S. Universe Leader, was built in 1956. She had 52 tanks in all and could hold over 1,300,000 gallons total (source).
Modern supertankers, like the very large crude carrier (VLCC) class, are able to hold an estimated 84 million gallons or 2 million barrels of crude oil for every 318,000 metric tons. Ultra-large crude carriers, or ULCCs, which weigh up to 550,000 deadweight tons, can carry up to 4 million barrels (source).
Barrels and Drums per Metric Ton
In contrast to the American Stock Exchange which measures oil in barrels, the European Stock Exchange reports the volume of oil in metric tons. If you know the API gravity of the oil carried, you can calculate the rough amount of barrels per metric ton. You simply add 131.5 to the API gravity and divide by the product of 141.5 and 0.159.
Going back to our benchmarks, we get 7.6 barrels per metric ton for West Texas Intermediate, 7.54 barrels for Brent Crude, and 7.22 barrels for Dubai Crude. Using 55-gallons drums, we get 5.8, 5.76, and 5.5 for every metric ton respectively.
For heavy crude oil with an API range of 25 API to 10, we get 6.96 barrels per metric ton to 6.29 barrels per metric ton or 5.31 to 4.80 drums.
As you can see, the weight of a gallon of oil is directly dependant on its grade as measured by the oil’s API gravity. The higher the oil’s API gravity, the lighter the oil is and the higher its value is. Lighter oils produce higher levels of gasoline, diesel, and jet fuel, which is why they command such a high price.
While the threshold standards between light, medium, and heavy crude vary widely, that established by the Louisiana DNR is one of the most frequently cited. On average, a gallon of extra light crude will weigh 6.65 lbs/US gal, light crude 7.03 lbs/US gal, medium crude 7.398 lbs/US gal, heavy crude 8 lbs/US gal, and extra heavy crude will weigh about 8.5 lbs/US gal.