Biological diesel should actually be named 'Rapeseed methyl ester' (see above). Lately, its environmental friendliness is controversial. The fuel is extracted, in principle, from renewable raw materials which use up the same amount of carbon dioxides for their growth as is generated during their combustion. However, the relatively bad efficiency makes its usage as fuel questionable. Taking the high prices for crude oil into consideration, long transportation ways are economical, but the energy consumption for the complete transportation should be accounted for, actually. Growth potentials and profits are so tempting for some developing countries, e.g., for palm oil, one possible raw material for the production of biological diesel, that forests are cleared without decent thoughts about the people and animals living there, often taking their living space away. This is exactly the opposite of what we would like to accomplish by the usage of biological diesel.

Biological diesel can not serve as the solution for our environmental problems. For a country like Germany, there is simply not enough acreage for the production of a substantial portion of the annual fuel need. If diesel is once to contain 10% of biological diesel according to EU plans, this will be possible in Germany - with the present processes and surfaces - only with import. In addition, for the production of biological diesel - exactly like with other fuels - at least 20% of fossil energy is needed. The subsidies for the farmers are very high. The losses for the state are softened somewhat in 2006 by the EU due to a tax on oil of 15 cents per liter. At the present oil price biological diesel is not yet competitive. Another problem of biological diesel is that laughing gas evolves from the nitrogen fertilization which is still much more polluting than carbon dioxide. The energy insertion for the production of biological diesel must still be reduced.

The adjustments that are necessary for the car are limited, and sometimes the car producer is willing to do it against a low surcharge. For example, some wires need extra protection. The engine has slightly less power, yet no sulfur connections in the exhaust gas any more. Generally, the emissions (particles, CH and HC) are reduced. In addition, oxygen is included, an advantage for a very clean combustion in the engine.

Biological diesel is hygroscopic like brake fluid and works on varnished surfaces like a solvent. Operating the car with biological diesel must be explicitly allowed by the manufacturer, otherwise there is no guarantee in case of damages, e.g., for the fuel injection system, which can be expensive. The operation with pure biological diesel is not always without problems - not only in the winter period - with vehicles of the newer diesel generation, even if they are released by the manufacturer. Therefore, e.g., VW has withdrawn its clearance and adaptation kit, and recently even forbids the usage of this fuel. Care is required especially with summer-bio diesel in winter. At low temperatures it is anyways advisable to tank normal diesel oil or at least to add it, or to start the engine with diesel oil. Although the cetane number of biological oil is higher, the heat value is slightly lower. This may imply up to 8% of additional fuel consumption.

There is a future for biological diesel as additive; it is added to the normal diesel oil up to a maximum of 5%. It does make us less dependent on the imported crude oil, promotes the home agriculture and probably contributes to the climate protection. Production and use of biological diesel raise the acceptance of synthetic fuels which are substantially more promising in terms of efficiency.