Pseudomonas oleovorans was grown on 2-methyl-3-hydroxyoctane, ethyl 2-methyl-3-hydroxyoctanoate, ammonium 2-methyl-3-hydroxyoctanoate, and methyl 2-methyl-3-hydroxyoctanoate in attempts to obtain poly(3-hydroxyalkanoate)s (PHAs), with methyl branches at the 2-position. The microorganisms did not grow on these carbon sources alone but survived and could be reactivated later with organic substrates which could be used for good cell growth. Futhermore, bacterial growth on the branched carbon sources was observed when a cofeeding technique was applied, in which case cell growth showed no lag time and formed a biomass which contained a high percentage of PHAs. In this manner a variety of copolymers were obtained, and these were investigated by NMR, methanolysis-gas chromatography, and thermal analysis. With nonanoic acid as the cosubstrate, the polymers obtained contained mainly 3-hydroxynonanoate and 3-hydroxyheptanoate units; this is the copolymer to be expected from the preferred consumption of nonanoic acid. In addition, however, a low percentage of units with 2-methyl substituents could be detected by NMR, and the incorporation of these unusual repeat units resulted in an observable change in the thermal properties of the PHAs.