Schwa, most of your questions would be answered by reading the link that was provided in the first post. It indicates that it would be very possible to meet the fuel needs of a nation even as large as the USA. Not without a significant investment, but it states it could be as cheap as "only" $46 billion a year compared to $100-150 billion already spent on oil imports.

As for Martin's question about emissions, most of the most harmful emissions aren't going to be present in biodiesel, they're usually from chemicals still left over in petrodiesel after refining. Those chemicals should not be present at all in biodiesel. Besides which, many people pan the Tier II Bin 5 emission standard as ridiculous and way overboard since currently we have NO mechanism for getting old vehicles off the road.

The emissions standard for 10-15 year old vehicles is no where near as stringent as current vehicles, yet if we really cared about emissions, we would just have to make it illegal to register a vehicle more than 10 years old. Until we reach that day, it's pointless to push our emissions standards any further than 2003 standards, basically, because that's already many times cleaner than all previous generations of vehicles.