Abstract: Methods of producing an unsaturated free fatty acid comprising at least 18 carbon atoms are provided. In some embodiments, the methods comprise culturing an engineered microorganism in a culture medium, wherein the engineered microorganism comprises at least one recombinant enzyme selected from acyl-lipid desaturase delta-9 (EC:1.14.19.1), acyl-lipid desaturase delta-12 (EC:1.14.19.6), acyl-lipid desaturase delta-15 (EC:1.14.19.-), and thioesterase (EC:3.1.2.14). Engineered microorganisms comprising at least one of those recombinant enzymes are also provided. The methods and organisms can be used to produce at least one free fatty acid selected from oleic acid, linoleic acid and ?-linolenic acid.