How efficient is organic alcohol produced from yeast fermentation as compared to distilled alcohol from crude oil as a bio-fuel? Is it a viable alternative?

Alcohol is a poison so, in fermentation, it can only reach a concentration before it kills the yeast. This means that you're dealing with a much lower concentration, by which I mean that it's diluted with water, plus there's a lot of dissolved and suspended matter (the yeast itself, other chemicals consumed/produced by yeast, etc). I think all that water would present the greatest obstacle to overcome in order to use organic alcohol as a fuel.

Alcohol is always distilled. If not, it won't burn at all: it's as concentrated as in wine.

 

Alcohol is always mass-produced by fermentation of organic material: corn, sugar cane, sugar beet... Never from crude oil, which contains essentially hydrocarbons.

 

If the question is alcohol versus gasoline, the answer is "Brazilians use ethanol everyday in their cars". About as good, but the injector needs a specific adjustment. It's excellent for the Brazilian cane producers, and also for the inhabitants, as the exhaust gas is much cleaner - I testify from first-nose observation.

I agree with Enthalpy. Almost all ethanol is produced from sugar (from plants), through fermentation and distillation. So, yes, it is a viable alternative.