Article Ref: E-004 

Weights and Measures Connection, Vol. 3 , Issue 3 Page 1

PML technician Sherry 

Sheckels uses a flashlight 

and magnification loupe

to take exact water-level 

measurements on a stainless 

steel container.

June 18, 2012

Petroleum Volume: Getting Calibrations in the Can

Byline: John Wrights, Physical Measurements Laboratory, Sensor Science Division

The volume of oil and oil products moving through America’s pipelines, 

waterways, roads, and rails borders on the unimaginable. “Look at it this 

way,” says John Wright, a Project Leader in PML’s Fluid Metrology Group. 

“Per capita consumption of petroleum in the United States is 10 liters per 

day. And there are 300 million people. That’s three billion liters moving 

around each day and usually being metered several times along the way. 

The infrastructure requirements are mind-boggling.” So is the value. 

Three billion liters is about 19 million barrels. And with crude oil priced 

around $100 a barrel these days, approximately $2 billion worth of 

petroleum travels from multiple sellers to multiple buyers every 24 

hours. Clearly, even tiny errors in measurement can amount to a great 

deal of money. 

To ensure maximum accuracy, the U.S. petroleum industry relies on 

volume measurements traceable to NIST, and specifically to the Flow 

Metrology Group in PML’s Sensor Science Division. Customers bring in 

their own “field test measures” – stainless steel containers ranging in 

capacity from four liters to 8 000 liters, made with graduated necks but 

informally called “cans” – to be calibrated. 

The cans are used to calibrate various “prover” mechanisms that 

measure movement of volume per unit time, and the provers in turn are 

used to calibrate various kinds of flowmeters. Because the provers and 

meters differ widely in capacity, a variety of can sizes is typically necessary.

For example, Alberta-based calibrators Glenn Antoniuk and Barbara Germin recently spent two weeks at 

NIST calibrating 13 cans ranging from 1 to 500 gallons. That may seem like a long time, but the process is 

laborious and painstaking. Each can is cleaned and thoroughly dried, carefully leveled, and weighed 

empty. Then the can is filled with purified water and weighed again. This entire process is repeated five 

times for cans of 380 liters or less, and at least twice for larger cans. 

“We often calibrate over 100 measures a year here, from all sorts of customers,” says Fluid Metrology 

technician Sherry Sheckels, “including some designed to be transported by barge out to offshore oil 

platforms for on-site calibrations.” 

Not surprisingly, there are industry standards specified by the American Petroleum Institute that govern 

each stage of the calibration operation. For example, cans smaller than 20 liters are drained by pouring 

through the neck while tilted to 70 degrees from horizontal (not 90 degrees, which is completely 

vertical) and there are standardized drainage and drip times. 
Article Ref: E-004 

Weights and Measures Connection, Vol. 3 , Issue 3 Page 2

Two customers prepare their 

“cans” for calibration in PML’s 

Fluid Metrology facility.

John Wright of the Fluid Metrology 

Group examines apparatus newly 

arrived from Mexico as part of an 

international volume-standard comparison.

Because the mass, density and temperature of the water are 

extremely well known, container volume can be determined to high 

accuracy after correcting for factors such as thermal expansion of the 

metal. The petroleum industry expects uncertainties less than 0.05 % 

for custody transfer or billing applications. NIST’s can-volume 

calibrations are in the range of 0.01 percent for very large cans. 

John Wright of the Fluid Metrology Group examines apparatus newly 

arrived from Mexico as part of an international volume-standard 

comparison. The other variable of intense interest is how the 

measurements change or “drift” over time. “If our calibrations or our 

customers’ calibrations or the pipe-provers’ change too much,” 

Wright says, “then there’s a lot of retroactive money that changes 

hands. It can amount to very large sums because the volume is 

extraordinarily high.”

Glenn Antoniuk, whose company conducts calibrations from western 

Canada down to the Gulf Coast, agrees: “I’ve heard of settlements 

that have been in the 

millions.” State laws 

governing the volumetric 

accuracy of products delivered to the consumer usually 

specify 0.5 % uncertainty, and end-point distribution has to 

be monitored from time to time. “Five gallon cans are used 

at gas stations by state labs to make sure that pumps are 

calibrated properly,” Wright says. 

Because petroleum and other products sold by volume can 

cross many national borders, it is highly important that 

international standards agree as closely as possible. This 

necessitates round-robin comparisons, and Wright is now 

preparing to test a set of precision containers from Mexico.

“In general, the agreement among different national 

metrology institutes is extremely good,” Wright says. “But that doesn’t mean we can ever stop 

measuring.”