Biolipids can be derived from plant, animal, oleagi­nous microorganisms and algal sources. The composi­tion of biolipids derived from each of these sources differs greatly and has varying degrees of suitability to the biofuel production industry. The major lipids produced from each of these sources are listed below and the degree of suitability to the production of biofuel production is discussed.

Plant-Derived Biolipids

In 2007, 95% of world biodiesel was produced via edible plant oils, which were supplied by the agricul­tural industry, with the vast majority supplied by rapeseed oil, 84% (Food and Agriculture Organization,

2008) . Overall, plant lipids are divided into three major categories: edible, nonedible and waste vegetable oils described below.

Edible Lipids

The main edible oils used for biofuel production are rapeseed, palm and soy bean oils. Edible oils have the disadvantage of competing directly with food produc­tion. The use of edible oils for the production of biodiesel competes directly with the use of land for the produc­tion of food and without proper planning results in reduced food production (Gui et al., 2008). However, the productivity from edible oils is high in terms of oil yield and the quality of the resulting biofuel. The oil yield from palm is the highest of the commonly grown edible oil crops at 5 tons per hectare while rapeseed produces 1 ton per hectare and soy bean 0.52 tons per hectare. A high lipid yield is vital for the economical production of biofuel from these plants. Although the productivity from palm oil is particularly high its use as a biofuel is limited as it is the world’s most commonly used edible lipid and thus competition for the oil between the food and biofuel industry would result in an increase in the price of this oil (Lam et al., 2009). In terms of the suitability for biofuel, palm oil has a high degree of saturation and thus is not the most suitable for biofuel production with the resulting fuel having poor cold flow properties. However, the cold flow prop­erties of a lipid can be altered by the use of cold filtration (Kerschbaum et al., 2008) or alternatively the use of alco­hols such as ethanol, isopropanol or isobutanol, which results in the production of fatty alkyl esters with lower freezing points and therefore improved cold flow prop­erties (Dunn, 2009). There are also some environmental and ecological concerns surrounding palm oil produc­tion, with the clearing of rain forests to make way for palm plantations. The plantation costs of edible oil crops are relatively low with the exception of palm oil, which has a higher cost; however, this is offset by the high oil yield from the crop. The overall estimated energy balance of rapeseed and soybean is similar at 3.7 and 3.4, respectively, while palm oil is significantly higher at 9.6 due to the high yields (Food and Agriculture Organization, 2008). Currently rapeseed oil is the most commonly used plant oil used in biodiesel production because it makes an excellent biofuel with excellent cold flow properties. The main disadvantage of using rapeseed oil is the growth of rapes is difficult and unsus­tainable as it must be part of a one in five rotation due to the large quantity of nutrients required for the growth of the organism and the buildup of pathogens and disease in the environment targeting rapeseed if grown annually.