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I was reading documents about energy importation and came across the following:

The import was of 5,915.87 MMtoe

I wonder if MMtoe = $10^6*10^6$ toe = $10^{12}$ toe.

First time coming across a unit expressed like that.

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    $\begingroup$ I don't see why you wouldn't just use 5915 Ttoe or 5.95 Ptoe. $\endgroup$
    – DKNguyen
    May 25 at 22:48
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    $\begingroup$ To consolidate and correct previous comment: M is sometimes used for 1000 in the US energy industry (don't know why), in particular with natural gas - e.g. Mcf, MMBtu and therefore MM is commonly used for 10^6. You also see MM used like this in finance sometimes. It is also my impression that in current industry use, "toe" is always tonnes i.e. metric, but I'm slightly less confident of this $\endgroup$
    – Pete W
    May 25 at 23:21
  • $\begingroup$ Did whoever wrote it use the SI unit system? If not they can define units as they want. $\endgroup$
    – Solar Mike
    May 26 at 4:16
  • $\begingroup$ Pursuant to the posted answer by NMech, can you provide a bit more context here? $\endgroup$ May 26 at 13:16
  • $\begingroup$ @CarlWitthoft I was wondering myself, about the document source . $\endgroup$
    – NMech
    May 26 at 13:56
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TL;DR: the MM in MMtoe is probably related to the Latin Numeral M (for 1000). In that context MM means one thousand thousands (i.e. one million)


Although this is very confusing, the bottom line is that to (my understanding)

$$ 1 \text{ MMtoe} = 1 \text{ Mtoe} = 10^6\text{ toe}$$

Where:

  • 1 toe = 11.63 megawatt-hours (MWh)
  • 1 Mtoe = 1 MMtoe= 11.63 terawatt-hours (TWh)

Metric Ton or Tonne interpretation

To my (initial) understanding (I am willing to bet to a lot of other people accustomed to SI units):

  • MMtoe stood for "Million Metric Ton of oil equivalent".
  • Mtoe stands for "Million Tonne of oil equivalent".

So, I thought that the confusion arose because:

  • There are many ton units (see below)
  • "Metric Ton" is a "Tonne",
  • 1 toe is defined strictly as Tonne of oil equivalent

Brief description of Ton units

This is a brief explanation of the ton units.

  • the metric ton (which is relevant in the context of toe), is equal to 1000 kilograms, or approximately 2204 pounds. The metric ton is officially called tonne. The SI standard calls it tonne or Megagram (Mg), but the U.S. Government recommends calling it metric ton.

  • The British ton is the long ton( or displacement ton), which is 2240 pounds, and

  • the U.S. ton is the short ton which is 2000 pounds.

Both the long and short tons are actually defined in the same way. 1 ton is equal to 20 hundredweight. It is just the definition of the hundredweight that differs between countries.

  • In the U.S. there are 100 pounds in the hundredweight, and
  • in Britain there are 112 pounds in the hundredweight. This causes the actual weight of the ton to differ between countries.

Latin Numerals Interpretation

Then after some prodding from PeteW comments, I looked around a bit, and found the following link. And it actually gets even more confusing.

It actually goes says that the $M$ is the Latin Numeral for 1000 (and not from Mega = 1000000). And that $MM$ stands for one thousand thousands (ie. one million).

That explains why, McF, and MMBtu are used in the manner they are used (and probably even MMtoe is the same because it seems to apply to energy units).

Bottom line

Despite all this (inconsistency, arbitrariness and -at the end of the day- just plain craziness), the bottom line is that MMtoe (irrespectively to the interpretation you use) is equal to 1 million tonnes of oil equivalent.

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    $\begingroup$ If I didn't know any better, I would think whoever insisted on calling it million metric ton and then naming it MMtoe was someone in the US who just wanted to make the metric system seem as confusing as possible so no one would use it. I can see of no other scenario where someone sane would use the M prefix in such a way. Reminds me of the acronym NSR. Now...did that mean Nuclear Safety Related or Not Safety Related? Makes a big difference. $\endgroup$
    – DKNguyen
    May 25 at 23:04
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    $\begingroup$ @PeteW thanks for sharing your alternate life experience. It helped me learn something new, and connect a few more dots together. $\endgroup$
    – NMech
    May 26 at 6:07

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