NOVELTY - Producing hydrocarbons comprises: culturing an engineered cyanobacterium in a culture medium, where the engineered cyanobacterium comprises recombinant acyl-acyl carrier protein reductase (AAR) and alkanal decarboxylative monooxygenase (ADM) enzymes; and exposing engineered cyanobacterium to light and carbon dioxide, where the exposure results in conversion of carbon dioxide into n-alkanes, which include at least one of n-tridecane, n-tetradecane, n-pentadecane, n-hexadecane and n-heptadecane.    USE - The method is useful for producing hydrocarbons, which are n-alkane (including n-pentadecane, n-heptadecane (both preferred), n-tridecane, n-tetradecane or n-hexadecane), n-alkene or n-alkanal (including n-pentadecene, n-heptadecene or 1-octadecanol) (all claimed), which are useful as fuels and chemicals.    ADVANTAGE - The method: provides culturing host cells for direct product secretion for easy recovery without the need to extract biomass; enables production of various defined chain length of hydrocarbons and alcohols, where the secreted products are easily recovered or separated; and provides the products which can be used directly or with minimal processing.    DETAILED DESCRIPTION - Producing hydrocarbons comprises: culturing an engineered cyanobacterium in a culture medium, where the engineered cyanobacterium comprises recombinant acyl-acyl carrier protein reductase (AAR) and alkanal decarboxylative monooxygenase (ADM) enzymes; and exposing engineered cyanobacterium to light and carbon dioxide, where the exposure results in conversion of carbon dioxide into n-alkanes, which include at least one of n-tridecane, n-tetradecane, n-pentadecane, n-hexadecane and n-heptadecane, where the amount of n-alkanes produced is 0.1-5% dry cell weight and at least two times the amount produced by an otherwise identical cyanobacterium, cultured under identical conditions, but lacking recombinant AAR and ADM enzymes. INDEPENDENT CLAIMS are also included for a composition comprising either: an n-alkane; or n-alkene or n-alkanal, which are produced by the method.