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Quick Breakdown: Vegetable Oil versus Biodiesel

Many people when they first see The Big Green Bus think that it runs on biodiesel, but in fact it runs on straight (used) vegetable oil. Vegetable oil is a component of biodiesel, which makes confusing the two quite easy, but they are actually different. Presently, a lot of debate exists over the merits of one versus the other, but each fuel type has the potential to move us away from fossil fuels, making a basic understanding of the resources important.

Vegetable Oil (SVO/WVO)

Vegetable oils, as the name suggests, are a form of biofuel derived by crushing plant matter. Many plants, including soybeans, rapeseed (canola), switchgrass, peanuts, and palms contain oils that can be used as a fuel. The energy contained in a given vegetable oil depends on the type of plant from which it came, but the most common VO in the United States (soybean) has about 5% less energy per volume than a comparable amount of regular diesel.

When used as a fuel (as in The Big Green Bus), straight vegetable oil is unrefined. Because it is left in its natural form, it is about eight times thicker than diesel at room temperature. At higher temperatures vegetable oil thins. Therefore running WVO in a vehicle means modifying the engine's fuel system to include a second, heated WVO supply. The Big Green Bus utilizes a technique that has been around for years with some custom touches (more info).

Biodiesel (B20/B100/etc.)

The difference between WVO and biodiesel is largely a philosophical one (although there are certainly technical and practical considerations as well). Whereas straight vegetable oil requires a modified vehicle to be used, biodiesel is modified vegetable oil that can be run in a stock diesel vehicle. A chemical process called transesterification switches one part of the VO chemical structure with an alcohol. The result is a fuel based on vegetable oil that is less thick at low temperatures. It therefore does not require special heating before an engine can use it.

So why bother with straight vegetable oil at all? There are a number of reasons, which spark back and forth debate between ardent SVO users and biodiesel users. One important factor is that the chemicals used in biodiesel production are quite toxic and must be handled carefully. The chemicals and energy required to produce biodiesel also mean that less energy is released by the fuel (to drive your vehicle) compared to the energy required to make it in the first place. Biodiesel, however, is a definite improvement over fossil diesel because it requires less refining (and therefore less input energy) and can be derived from locally-grown vegetable oils. Local feedstocks reduce the energy and costs of transportation and support the local economy. Unfortunately most biodiesel available in the United States is a blend of 20% biodiesel and 80% regular diesel (known as B20). B20 represents a definite step forward, but it still contains mostly fossil fuels. The finite availability of fossil fuels demands that biodiesel reach 100% blends in order to be anything more than a short-term solution. Presently, the greatest obstacle before B100 are car companies' reluctance to use different gasket materials in their engines (a simple task) and to offer warrantee coverage. A national B100 standard (comparable to the standard recently enacted for B20) will likely be a necessary stepping stone before automakers embrace the fuel.

Quick Fuel Comparison Chart


Vegetable Oil


MADE from filtered vegetable oil

IS filtered vegetable oil

Refined from petroleum in an energy intensive process

Can be used in ANY diesel vehicle

Can only be used in a diesel vehicle modified (more on that later)

Can be used in any vehicle diesel

Effects due to fuel not covered under defects/workmanship warranty; Recommended biodiesel blends vary by manufacturer

Effects due to fuel not covered under defects/workmanship warranty

Effects due to fuel not covered under defects/workmanship warranty

Can be blended with diesel to produce B5, B20, etc.

Typically not blended with diesel

Can be blended with biodiesel

Costs more per gallon than regular diesel

Costs MUCH less than either biodiesel or regular diesel

Currently costs less than biodiesel, but costs are rising

Can be made by anyone from filtered veggie-oil, but it requires a safe work area and special equipment and chemicals

Usually gathered from cooperating restaurants and filtered by SVO vehicle owner


Can start in a cold engine; no switching fuels

Cannot start in a cold engine; must be preheated usually with heat of the engine running on diesel


Environmental Issues (Emissions, etc...)

Burning any fuel for your vehicle creates emissions that pollute the environment. But people still have to get places, so the idea is to minimize the amount of emissions that we create by burning our fuel. Using waste vegetable oil or biodiesel instead of petroleum based fuels such as diesel or gasoline reduces the total amount of harmful chemicals we release into the atmosphere. So what are the actual improvements in emissions that we can make by using vegetable oil based fuels?

  • Biodiesel (B100) and waste vegetable oil can be carbon neutral fuels. This means that the amount of new carbon dioxide emitted during burning was previously absorbed by the plant that was used to make the veggie oil. In effect, no new carbon dioxide (a greenhouse gas that is largely responsible for global warming) is introduced into the atmosphere. When we burn fossil fuels such as gasoline we are effectively unearthing and emitting carbon dioxide that has been stored beneath the earth for millions of years. However, the current means of producing vegetable oils for fuel consumes some fossil fuels, which prevents biodiesel or SVO from being completely carbon neutral from a system viewpoint. Waste vegetable oil is far closer to carbon neutral because one could argue that the resources consumed to produce the vegetable oil for cooking are sunk costs (although still warranting attention). Inefficiencies then arise from the collection means of the waste oil.
  • The crops currently used for biofuels in the United States are resource intensive. Corn requires significant fertilization (nitrates), and soybeans require large tracts of land.
  • Vegetable oil has slightly higher particulate emissions (the stuff that causes smog) than diesel, and biodiesel. However, biodiesel releases fewer particulates than regular diesel
  • Vegetable oil and biodiesel emissions are virtually sulfur-free. Burning either fuel releases less sulfur (which is one of the main causes of acid rain) than diesel.
  • Biodiesel and vegetable oil release fewer hydrocarbons than diesel.
  • Biodiesel and vegetable oil release less carbon dioxide and carbon monoxide than regular petroleum based diesel.
  • Vegetable oil and biodiesel emit about 10% more NO 2 than regular diesel but less SO 2. These two emissions operate inversely due to the temperature at which the fuel is burned. The more NO 2 a vehicle emits, the less SO 2 it will release, and vice versa.

So which one is better? That is a debate with no immediate conclusions. But both fuels have the potential to be viable energy sources within their own niches as demand spurs increased infrastructure, but neither will fully replace gasoline. We may now be accustomed to simple, singular solutions, but the reality is that any viable future energy system will be built on a wide range of fuel sources that can be broadly drawn upon.

Will vegetable oil power all of our cars?


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