^^ added an old video of e30 335i in previous post
LPG - Liquefied Petroleum Gas
http://www.nett.ca/faq/lpg-1.html the system costs about 1500$ so you have additional tank in your trunk and you can still drive on petrol or on LPG, when you out of LPG you switch back to petrol. Consuption is a bit higher but the price of LPG is 2x lower.
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"...free your mind and the body will follow..." - THE MATRIX