This title might suggest a learned dissertation on the symbolism of the mother figure in The Wizard of Oz or, for that matter, the Bond films of the 21st Century, but it is nothing so artful.

‘Disambiguation’, I have just learnt, is Wikipedia-speak for what in normal English might be called ‘clarification’. It is, according to Wikipedia, “the process of resolving the conflicts that occur when articles about two or more different topics have the same ‘natural’ title”.

Because ‘tea’, for instance, can mean not only the drink itself but also the formal afternoon occasion on which it is drunk and the informal evening meal at which it might or might not be drunk, persons seeking information on the drink might find themselves reading about other meanings of the word and could, thereby, become disoriented and fall idly about and be terribly in need of a cuppa, To avoid this possibility, Wikipedia has a disambiguation page explaining these various meanings.

Lord knows, the Oxford, Cambridge, Webster and other dictionaries have been explaining the multiple meanings of words for centuries without such a term but, hey, it’s 2007 and why use a perfectly good and established word when you can make up your own.

However, I accept that the effort is meant to avoid ambiguity and, while I hate the word, I agree wholeheartedly with the principle – in which vein, I want to do some disambiguating of my own about ‘M’. Actually, about ‘MM’ and ‘m’ and ‘mm’ too, so there is a lot of ambiguation that needs some serious dis-ing.

The petroleum exploration industry is fraught with uncertainty and we have to cling to constancy where we can. For instance, we measure oil in barrels. We write this as ‘bbl’. We like our barrels to come in the millions. We write that as ‘MM’. When these symbols are taken together, MMbbl, we have ‘million barrels’ in oil-speak.

I know officialdom in places such as Australia insists on using the metric system but no one takes much notice. Ask the person next to you at the next PESA function to tell you the potential reserves of the prospect they are working on. Ten dollars to a brick says they’ll answer in barrels and 90% won’t be able to tell you what it is in cubic metres.

The use of the barrel as a measurement for oil began in the USA in the 1860s, when oil was stored and shipped in wooden barrels. Initially, the most commonly used were whisky barrels, containing 40 gallons but 42-gallon barrels (based on the old English wine measure, the tierce) were also used. After Standard Oil adopted the 42-gallon barrel, the US Government made that the official unit of oil volume and it has remained so ever since.

The symbol for barrel has been ‘bbl’ since at least the late 1700s. It is not ‘bl’, which is the symbol for bale. It is certainly not ‘b’: a ‘b’ is a ‘barn’ to nuclear physicists and a barn is a b#* to any farmer who has to paint one. (Of course, the nuclear physicist is talking about the area of deflection of electrons bombarding a nucleus, but let’s leave that for another time.)

Why ‘bbl’? Some suggest it originated as ‘blue barrels’ because Standard Oil’s barrels were blue. This is nonsense: the abbreviation predates Rockefeller by almost a century. It is also suggested that it was chosen to avoid confusion with bale. That is an admirable idea, but why not “brl’. Don’t know. Don’t care.

The fact is that ‘bbl’ has been the abbreviation for ‘barrel’ for several centuries and there is no confusion about its meaning and no reason to use anything else unless the new term makes things clearer.

Similarly, MM is the accepted oilfield notation for one million. Which gives us ‘MMbbl’ for ‘million barrels’. Very simple. Good oilfield practice.

The use of ‘MM’ as the oilfield symbol for million almost certainly comes from the Roman numeral system. The purists will agree that the Roman numeral M represents 1000 but rush to tell me that MM is 2000, not 1,000,000. That’s true, but the Romans weren’t all that consistent about how they used some of the symbols, especially when it came to numbers larger than one thousand. Five thousand could be written MMMMM but it could also be VM and, in the extreme, something more like I))).

Forced to decide how to express one million, the purists might have gone for ((((I)))) [each parentheses is a factor of 10, and the central (I) is 1000] but Remus and the boys down at the tar pits would have been happy with MM – and I think those Pennsylvanian oil-boys probably figured the same.

Regardless, it’s the symbol we use and as long as we use it, we know what we mean.

I can understand that some people, especially our European friends, might want to use the symbols of the International System of Units (abbreviated to SI, from the French Systems international d’unites). The SI prefix for a million units is ‘mega’ and the symbol is ‘M’.

The problem with this is the ambiguity it creates. I recently had a geochemical report stating that low thermal maturity of the source unit meant that large volumes of oil had not been generated, with the amount calculated at only 200 Mbbl. I assumed this was thousands of barrels but it was actually millions!

Regardless of its correctness as an SI symbol, ‘Mbbl’ will mean ‘thousand barrels’ to many, if not most, oilfied people, and that will cause confusion. Mind you, it also means ‘Mounted battlespace battle lab’, Google tells me.

My interest in this subject was sharpened by that geochemical report but it began with my noting over recent months a move in both Australian and UK newspapers and magazines to use ‘m’ for million. Lower case ‘m’! And without a space, as in 123m. This is simply wrong and should not be used.

There is no justification for this use of ‘m’ for million; ‘m’ is the abbreviation for metre and I cannot fathom why any editor would allow it to be used for million. Yet this is now common in, for example, the Economist, which is considered quite erudite by its readers (notwithstanding references to the ‘English queen’ small ‘q’).

Government promises 10m, the headline says. Are they going one better than the whole nine yards, you ask? No, it’s a funding grant!

This is also coming into our industry. A website (www.exileresources.com) I looked at recently said that Nigeria has total reserves of ‘36 bn bbls’, and is producing at a rate of 2.45 mmb/d! What a dog’s breakfast of symbols that is!

Firstly, ‘bbl’ is plural in itself; there is no need for the ‘s’. Secondly ‘mm’ is a number only in the Arabic numeral system when it means 2000. Otherwise ‘mm’ is the SI abbreviation for millimeter and ‘mb’, for millibars.

I know we know what ‘mmb’ means, but that’s no reason to accept it. Inconsistent or arbitrary use of symbols can only lead to confusion and has no value to us as scientists or writers.

Peter Purcell.