Just to clarify where the original numbers came from...

The claim you are responding to: 1 liter of oil ~ 3 days of human energy output.

Energy in a liter of oil: about 30 megajoules.

Human base metabolic rate: below 100 watt. Let's say 100 watt. 1 watt = 1 joule/second.

30 MJ / 100 joules/second = 300000 seconds = about 3.5 days. So the original claim is correct in that sense

edit: Now, this doesn't mean you can get the same benefit from a human laboring for 3 days non-stop as you could get from 1 liter of oil. This is just the energy required by the human body to stay alive. Any additional useful energy output would be on top of that, and humans can only sustain a small amount of additional power for long. That's why your references seem to disagree.

Though you will really get that 100 watt from a human in the form of heat, which is why that number needs to be used when designing airco systems.

I came to understand how much power is in oil through digging a big hole. I had to do some excavation for a mountain cabin I am building. After digging by hand for a while, we bought a 1-ton micro-excavator. One bucket from the excavator is equivalent to about 10 shovels. The avg time per scoop is similar, and it burns half a tank per day, so it works out such that it does the work of about 10 men on around 10 l/day of diesel.

Thus I discovered that 1 liter of diesel can do about 1 man-days worth of dirt moving. This liter costs about $1 right now. A day laborer would cost around $160-$250.

After digging hard ground by hand where you have to fight for each shovel full, seeing the tiny excavator rip 100lbs of earth like a toddler playing in the sandbox makes you appreciate what a gift oil is. Bigger excavators with better operators are more efficient. I would not be surprised if a big one approaches the 9man-days / liter theoretical limit you calculated above.

If you want a really big multiple, use the liter of fuel to run a generator to run epyc cpus performing calculations and compare it to humans performing calculations.

The value I gave hugely understates oil's useful energy. Even so, the energy equivalents shown are huge.

But if you want greater accuracy:

A human being consumes ~2000 -- 3000 kilocalories per day.

A human produces only a fraction of that in useful work output:

- Total metabolism is only so efficient, I believe on the order of 25%.

- That 2000 -- 3000 kilocalries/day gives you 96--145 watts constant output. That's where the "a person produces 100 watts of (thermal) energy at rest comes from. About 1/4 of that, 25 watts, is required simply for your brain.

- People can work only so many hours per day, and at relatively low constant output.

The net available work is probably closer to 1/10 to 1/4 the net output. So a litre of oil -> 30 days of actual delivered effort by a human.

Of course, burning oil for mechanical energy results in about 70% losses through Carnot efficiency, so we can divide by 3 and get about 10 days of useful mechanical energy, roughly 3x greater than the raw dietary comparison I'd made above.

On the true cost of oil, I'd make another argument which is that if we consider costs to represent the true costs of production, then the fact that oil is created through an immensely inefficient conversion of ancient sunlight to biomass to kerogenic materials over hundreds of millions of years, and we're extracting it at roughly 5 million times its rate of formation, the production cost value should be about 5 million times that of present biomass.

The PeakOil discussion is looking at the net value basis. That also increases the price, but "only" by a factor of thousands, not millions.

If you look at the delivered GDP per barrel of oil (dividing national GDP by oil consumption), what you find for most countries is a value somewhere between $400 and $3,000/bbl. The lower values are for India and China. The US tends to see about $1,000 GDP/bbl, most of Europe $2,000/bbl, and Switzerland about $3,000/bbl. Some poor, low-oil-consumption nations do better (Mali did when I last looked into this), but that's more a testament to how little oil they consume rather than how efficiently they process energy in bulk.

Given valuation of $0.5 -- $5 million based on actual work / true cost of formation, use of oil as presently practiced is absolutely noneconomic. It makes about as much sense as burning $100 bills for heat. (I'm presuming non-inflated currency.)

Very solid answer, thanks, and also to @wcoenen

> " One barrel of oil has the same amount of energy of up to 25,000 hours of hard human labor, which is 12.5 years of work. At $20 per hour, this is $500,000 of labor per barrel "

Why use humans for physical power output? Humans invented watermills millenia ago.

I struggle to understand your thinking. The point is to put energy measures in terms that are intuitively understandable by people, and the most comprehensibly to people is human-power. Perhaps when Ikea produce a line of watermills we can revisit your rather odd question.