For what it's worth, the Conoco station at Hwy. 93 and Eldorado Canyon (a few miles south of Boulder city limits) just started selling bio-diesel. I've been running a 20% mix in the PSD as an experiment and I'm very pleased with the stuff. Engine starts noticeably quicker, so the cetane rating is good, and the truck boogies along real well on it, the same as summer diesel. Bonus: The exhaust sort of smells like french fries cooking.
It's an oily, light brown liquid and it doesn't foam like petro-diesel. Reportedly, it adds lubricity to the fuel like Stanadyne, even when used at less than 5%, that's a good bonus.
The station manager said it's made by a company in Englewood, so maybe it's available in the south metro area?
Anyhow, that's where to find it if your oil-burner is in the area and you want to try some.