Biodiesel and Synthetic diesel

Biodiesel is a fuel manufactured from vegetable oils and fats, through a process called transesterification. It is also referred to as FAME (Fatty Acid Methyl Ester). The most common basis is rape seed or sunflower, which can be blended with conventional diesel. 

The energy efficiency well-to-wheel is low but it also produces more NOx emissions with the present vehicle fleet. However, CO2 emissions decrease by about 60% compared with regular diesel, although there is limited potential for production of large quantities. 

Note: Volvo's products are today compatible with biodiesel when blended into diesel.
Synthetic diesel
Synthetic diesel is a mix of synthetically produced hydrocarbons made by gasification of biomass, which can be blended into conventional diesel. Technically speaking, this fuel is also a type of biodiesel but is treated separately for practical reasons.

There are several sources and it has a variety of uses. It has lower energy efficiency than other synthetic gas products and the current production is very limited. Synthetic diesel is fully compatible with existing Volvo engines.