Pseudomonas oleovorans was grown on 6-methylnonanoic acid (B-MNA), 7-methylnonanoic acid (7-MNA), and methylnonanoic acid (8-MNA), 9-methyldecanoic acid (9-MDA), 7-methyldecanoic acid (7-MDA), and 2,6-dimethylhept-5-enoic acid(2,6-DMHA). Poly(beta-hydroxyalkanoate)s (PHAs) were obtained when this bacterium was grown on pure 9-MDA, 8-MNA, 7-MNA, and B-MNA, but not on 7-MDA and 2,6-DMHA. The mixtures of n-nonanoic acid (NA) and either 7-MDA or 2,6-DMHA gave almost pure nonanoic acid homopolymers. For the other branched substrates, H-1 and C-13 NMR studies showed that the polymers obtained contained the type of methyl branching expected from the starting alkanoic acid. The melting points of most polymers were similar to that of nonanoic acid except for that of the polymer from 6-MNA, which was considerably higher. DSC measurements also showed that this polymer crystallized much faster than the others. C-13 NMR spectra of the polymer containing 6-methyl-3-hydroxynonanoate units showed that equal amounts of the two chiral isomers were present. From the GPC measurements the number-average molecular weights (M(n)) of the polyesters produced were in the range of 70 000-384000 with polydispersity indices (M(w)/M(n)) in the range of 1.37-2.55. Wide-angle X-ray diffraction measurement revealed that the crystalline structure of the polymers obtained from 6-MNA was different from that of the polymer obtained from n-nonanoic acid.