I did a very similar calculation in an article for the oildrum a few years back.

I agree that in order to compare apples to apples, you have to measure human output, not input. I used the wattmeter on Floyd Landis' bike (the Tour de France winner accused of androgen use), which registered 230 watts average for the whole riding time of the Tour. I divided by 2 for us less-in-shape people, and then assumed you could put out that power for 6 hours a day on weekdays (not counting breaks).

On the barrel-of-oil side, I used 20 gallons of gasoline from a 42 gallon barrel. Once again, you have to measure useful power output, not input calories, so I assumed it was being burnt in a 25% efficient engine in a car or piece of oil-powered equipment.

That works out to one barrel equals one year of human work. Of course, a human with a brain (which, incidentally, runs on 5-10 watts) could use that power output more strategically -- e.g., by pulling individual weeds instead of a plow -- but sometimes, you just need the power output straight up -- like when a load of concrete is hoisted up to the top of a building, or old concrete is crushed into gravel.

In the article, I also noted the difficult situation with non-renewable helium, given that I mostly do MRI for a living.

Marty

Looks like a violation of thermodynamic laws if you truly believe humans convert energy to work at 15-30% efficiency. The temperature difference between core body temperature and the skin is only 17 kelvins. With perfect mechanical efficiency that works out to only 5.48%. As the load increases the difference between core and skin temperature may decrease causing efficiency to drop further. From this low figure the energy needed for basal metabolism needs to be included. That 12% at the wheels starts to look pretty good.