The Energy Returned on Energy Invested (EROEI, affectionately) is a sort of master indicator of dependency, but it registers natural limits. It takes a lot more energy to produce tar sands than conventional oil. Corn ethanol, touted as a solution to the emissions problem, actually expends more energy than it produces.
For a different way of expressing the investment-return ratio, take a look at this somewhat fuzzy chart from oilreport.org, which is measuring an "Energy Profit Ratio." In the 1920s, oil yielded 100 times the energy it took to obtain and process it. According to the chart, ethanol, nuclear, wind, and tar sands do poorly today on what seems to be simply a measure of the EROEI. This is a pretty good chart, if you ask me, even if I can't read half of it.
One note of caution: the "energy/profit" ratios are changing for oil, and are biased if they give much weight to Persian Gulf oil. "New oil"--that is, oil far off shore, in the deep seabed or in various other formidable environments--requires far higher levels of energy to extract.
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