Cask sizes and volumetric esoterica

In the British lexicon, casks are distinguished by size, as either fractions or multiples of a barrel (bbl). I find the names of the various cask sizes are amusing:

Pin - 4.5 UK gallons (1/8 bbl)
Firkin – 9 UK gallons (1/4 bbl)
Kilderkin – 18 UK gallons (1/2 bbl)
Half-hogshead – 27 UK gallons (3/4 bbl)
Barrel – 36 UK gallons
Hogshead – 54 UK gallons (3/2 bbl)
Puncheon – 72 UK gallons (2 bbls)

Coincidentally, most homebrewers end up producing batches of pin (4.5 gallon) or firkin (9 gallon) size. One of these days it would be fun to brew on a system cranking out hogsheads (54 gallons - 1.5 barrels) of beer!

This whole discussion brings to light the rather convoluted relationships of barrels to gallons on the two sides of the Atlantic. It seems that 1 US barrel of beer is 31 gallons, while the UK barrel is 36 gallons. However, the conversion from barrel to gallon is further complicated by the fact that a UK gallon is 1.2 US gallons. In order to compare the two barrels properly, it is therefore necessary to convert them both to liters. A US barrel is 1.17 hectoliters (Hl), or 117 liters. A UK barrel on the other hand calculates out to 1.63 Hl. To further confuse matters, the definition of a US barrel as given above ONLY applies for beer! A US oil barrel is 42 gallons (approximately 35 UK gallons), while a US barrel of any liquid except beer and ale is 31.5 US gallons (119 L). This is also referred to as half a hogshead, however a British half-hogshead would more rightly be converted as 32.4 US gallons (27 UK gallons). In addition, a US dry barrel is 105 dry quarts (115.6 L). Go figure.

Small commercial microbreweries generally use a setup of at least 10 bbl. Assuming those are US barrels, that's enough for 3000 12 oz bottles of beer! I still haven’t been able to ascertain for certainty, however, whether brewery output is measured in US or UK barrels, or both depending on the source, so a 10 bbl UK brewery could crank out as much as 4000 12 oz bottles. At this point, you may be asking “who cares?” You would be right. Who cares? I’m going to have a beer.

UPDATE: A-B apparently measures their barrels by the US standard, as they claim one barrel is 31 gallons (they crank out 16 million barrels a year - that's half a billion gallons!) Thanks to "Modern Marvels: Brewing" for the interview with one of A-B's reps. One other nugget from the A-B section of the show - they claim to actually use natural carbonation! I'm not sure how this works - do they filter, pasteurize, and package all under pressure? Seems like it would be easier just to force carbonate.