NOVELTY - Preparing (M1) a hydrocarbon involves contacting a fatty acid substrate with at least one fatty acid reductase, at least one fatty aldehyde synthetase, and at least one fatty acyl transferase, where the fatty acid substrate is a fatty acid, a fatty acyl-acyl carrier protein (ACP), and/or a fatty acyl-coenzyme A (CoA), to obtain a fatty aldehyde; and contacting the fatty aldehyde with at least one aldehyde decarbonylase enzyme.    USE - For preparing hydrocarbon e.g. alkene and/or alkane for producing biofuel and/or biochemical (claimed).    ADVANTAGE - The method is suitable for preparation of hydrocarbon, which allows de novo construction of a synthetic metabolic pathway for custom alkane biosynthesis capable of utilizing the cellular free fatty acid (FA) pool directly. By modifying the free FA pool it is possible to produce both fuel-grade and branched alkanes in a bacterial host from basic, renewable ingredients.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) a recombinant host cell (C1) comprising a fatty acid reductase, fatty aldehyde synthetase and a fatty acyl transferase;    (2) an expression vector comprising at least one of the polynucleotide sequences (SEQ ID NOs: 11-25), as available on WIPO website, or their complements, or a sequence which will hybridize under stringent conditions to any such polynucleotide sequence;    (3) producing (M2) an alkane involving hydrogenation of an isolated alkene produced according to the method (M1);    (4) producing (M3) a branched alkane involving hydroisomerization of an isolated alkene and/or alkane produced according to the method (M1);    (5) production of a biofuel and/or a biochemical involving combining an alkene and/or alkane produced according to the method (M1), or an alkane produced according to the method (M2) or (M3) with at least one additional component to produce a biofuel and/or biochemical; and    (6) use of a host cell as a biofuel/biochemical hydrocarbon precursor source.