CORRECTION: Since writing this post, I have discovered that the explanation of the origin of bbl given below is a popular myth. For an explanation, please see my subsequent post HERE.
I was watching the TV show "Dirty Jobs" with the kids tonight. The host was working in a whisky distillery when he asked, "Why is barrel abbreviated 'bbl'? Where did the extra 'b' come from?"
Interesting question, so I researched it and here's the short answer. In the early years of the oil industry in Pennsylvania, wooden barrels were used to ship oil. Barrels of the day came in all sizes, most were somewhere between 30 and 50 gallons, but the most common was the 40 gallon barrel. Buyers became frustrated at the lack of standardization, so in 1866 more than two dozen leading producers agreed that 40 gallons would be the standard measurement for oil sales. An extra allowance of 2 gallons per barrel was agreed upon to account for evaporation and leakage during transport. So by 1872, 42 gallons became the accepted national standard.
At first, the oil industry produced far more kerosene than gasoline. Kerosene was shipped in blue painted barrels and gasoline was put in red barrels. Because the oil industry was now using the standard 42 gallon barrel and kerosene barrels were more plentiful, the term 'blue barrel' was used to identify 42 gallon barrels verses barrels of other sizes. So it makes sense that 'bbl' became the abbreviation for blue barrel. Eventually they stopped painting barrels blue, but the abbreviation stuck.