[davidzweig]

Running personal cars on cooking oil was legal in the UK up to a certain number of litres/year. I think it was more an issue of taxation, I'm not aware that it creates additional polution.

[kolinko]

I just checked and you're right. In Poland it's also during taxation - the penalties for using that are due to taxation laws, not environmental laws.

[bombcar]

In the USA (and other countries) there's something called "red dye" which is dyed diesel for use on off-road farm equipment, much less taxes on it.

If they catch you with it in your truck (by dipping the tank) you get big tax-evasion fines.