When it comes to man hours, oil is a far more efficient energy source then growing any yearly crop. The problem with oil is that it takes millions of years of dense forest growth to equal what we're near exhausting in a few hundred years. The rate of consumption grossly outpaces the rate of replenishment.
Read your history and you'll see a progression from using crop oils, to whale blubber oils, to mineral deposit oils (the kind we use now), each more efficient in man hours to extract and distribute then the last, and with each there was an exponential growth in the human work output and human population.
The Earth doesn't need oil, humans need oil. We've built up a very large and complex economic infrastructure responsible for feeding, clothing, and housing billions more people then can be sustained with less efficient energy sources then oil.
The idea that we can maintain our current way of life by using ethanol from corn, or oil from hemp is a farce. There is simply not enough arable land available to produce enough oils, nor is there enough labor available to make it happen.