Can I really burn used vegetable oil in my car?

Is Vegetable Oil Worth the Cost?

Louise Bailey shows off a sample of homemade biodiesel derived from recycled cooking oil. Is this the future of our commute?
Louise Bailey shows off a sample of homemade biodiesel derived from recycled cooking oil. Is this the future of our commute?
Matt Cardy/Getty Images

We know that an engine can really run on vegetable oil, but is it worth the effort? In terms of financial value, it's almost certainly not. The cost of the engine conversion will be very difficult to recover in fuel savings. On top of that, the cost of vegetable oil is approximately the same as diesel fuel. Veggie oil might be cheaper depending on where you live or whether you can buy it in bulk from somewhere like a restaurant supply store, but it generally doesn't represent a major cost savings over petroleum based fuels.

What about all that talk of getting used vegetable oil for free from restaurants? If you can get your fuel for free, wouldn't that represent a huge savings? It would -- for now. Right now, veggie oil is used as fuel by a relatively small number of hobbyists who like tinkering with their engines and adjusting their vehicle's fuel ratios. It won't take long for the restaurants to realize that used cooking oil is becoming a hot commodity once more and more people start asking for it. The free fuel supply will disappear quickly. Make no mistake: The amount of cooking oil discarded by restaurants every day may seem like a lot, but it's nothing compared to the millions of barrels of fuel Americans consume every day [source: Energy Information Administration]. There's no way used vegetable oil could ever become the primary way we fuel our vehicles, and there's even less chance it would ever remain free.

Unfortunately, there's really no way to save money by running on vegetable oil, but there might be other reasons to use it. There are no widespread statistics available for veggie oil mileage rates, but anecdotal evidence suggests that users could expect a mileage increase of up to 20 percent. There are a lot of variables involved, so true mileage increases could vary significantly.

Despite the economic pitfalls, there are environmental advantages to using veggie oil as fuel. Vegetable-based fuels burn cleaner and are non-toxic. Unlike fossil fuels, they're produced using renewable resources. Using modern agricultural techniques, we can grow lots of soy. Is it enough to fuel all the world's vehicles? Time will tell.

In light of these benefits, it might seem like a good idea to start converting all vehicles to run on vegetable oil. Before we condone such a large-scale change, it's worth considering the potential unintended consequences. We've already seen that increased use of fuels made from food crops - for example, ethanol, which is made from corn and sugar -- can drive up food prices. This increase in food-based fuels can also lead to the destruction of rain forests as farmers slash and burn countless acres to make room for newly profitable soy fields. As much as we want and need viable solutions, it looks like there are no easy answers to our energy problems.

For more information on alternative fuels and other related topics, see the links on the following page.

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  • Addison, Keith. "Straight vegetable oil as diesel fuel." (8/24/2008)
  • Energy Information Administration. "U.S. Product Supplied for Crude Oil and Petroleum Products." (8/23/08)
  • Freeman, Huey. "State makes big fuss over local couple's vegetable oil car fuel." Decatur (Ill.) Herald and Review. March 1, 2007. (8/25/08)
  • Henderson, Bruce. "Driver ticketed for using biofuel." The (Charlotte, N.C.) News and Observer. July 11, 2007. (8/25/08)
  • Lee, Margaret Juhae. "Green Cars." National Geographic. July 2005. (8/23/08)
  • National Biodiesel Board. Biodiesel Basics."
  • Tickell, Joshua, et al. "From the Fryer to the Fuel Tank: The Complete Guide to Using Vegetable Oil as an Alternative Fuel." Biodiesel America, 2000.