This is way too funny

, but enormously valuable.
I see your problem, you seem to be looking at this as a ratio rather than growth, and thus you are right you can't have negative values.
The missing ingredient is the lack of a definition of zero (0).
1 barrel in to 1 barrel out is zero growth, this then defines zero.
It may seem arbitrary, but you need to set it someplace. Much like zero celsius is arbitrary but valuable none the less.
You then can indeed have a negative return on investment.
The point of this argument is, as you've so eloquently mentioned, for the benefit of us great unwashed mathematically ignoramouses.
We don't feel comfortable with the notion that spending more than we get in return is seen as a positive.
And let's not get into how mathematics is the most damaging thing to civilization next to religion.

There is likely a ratio for it though
$this->bbcode_second_pass_quote('emailking', '')$this->bbcode_second_pass_quote('RdSnt', 'H')uh?
If you expend 2 barrels of oil and get back 1 barrel, you are short one whole barrel of oil.
If you expend 5 barrels of oil and get 1 back you are short 4 whole barrels.
Where's the fraction in that. I don't care what the proper, mathematical, statistical, defininition is. We are still talking about big, fat, heavy, round, whole barrels of oil.
Quibling about proper nomenclature is another waste of barrels of oil. Wonder what the ROCNAD (Return On Clarity from Nitpicking Academic Definitions) is of that?
Let me put it to you this way: if everyone understood math sufficiently well so as to see the difference between division and subtraction in the calculation of Enery Returned
Energy Invested, then we may have collectively addressed the PO issue a long time ago.
It's almost like you're insulted that you got it wrong...playing it back on us for trying to clarify. Words do mean something. Defintions do mean something.