Fatty acids are by far the most abundant lipids occurring in bacteria, microalgae, higher plants and marine fauna. Fatty acids occur predominantly as glyco- and phospho-lipids, although other unsaturated long-chain alkene precursors have been identified in the cell membranes of algae. These include: (i) a range of long chain unsaturated alkenes reported in bacillariophyceae (diatoms) of which C21:6 alkene is reported to be one of the most abundant hydrocarbons of the total hydrocarbon fraction in cultures (ii) C25-27 n-polyenes and C30 and C34 n-alkenes also found in diatoms (iii) C37-C39 alkenones biosynthesised by haptophyceae and bacillariophyceae (diatoms) (iii) C27-C31 alkadienes and alkatrienes ultimately biosynthesised by the race A of the freshwater alga Botryococcus braunii (Chlorophyceae) (iv) hexatriaconta-9,15,22-triene reported in microbial mats (v) long chain unsaturated alcohols (1,15 C32:1 and 1,19 C36:1) reported in Nannochloropsis salinia.