[sandcruiser]

personally, I burn about 20 gallons a month.... if I thought it was viable/cost effective to extract the oil, I'd start an algae culture in the backyard and run my septic system through it.

But I get the impression that extraction is the tricky part with algae.

As it stands, I'm thinking about planting some jatropha both here at home and on some ranch land nearby, then harvesting the seeds for oil. Even if I can get 5 gal/month out of it, that's 25% of my average fuel bill.

My figure above, 300 gal for 3 families, was aimed at people living in north america, two adults each commuting an hour each way (or running around w/ kids activities, or what have you), and using heating oil to keep themselves warm all winter. But I didn't put much thought into it, and you are correct that it would probably sustain many more than 3 families.

It would be neat if algae to oil production could be scaled to serve a small community- church group, work buddies, hardware store, what have you. To me, one of the biggest problems with fossil fuels has got to be that a huge amount of fuel is burned, just to get fuel delivered to where people can pick it up and burn it. Wasteful. But petro fuels just don't lend themselves to small-scale, local production.