The combination of plant oils and 3-hydroxyvalerate (3HV) precursors were evaluated for the biosynthesis of polyhydroxyalkanoate (PHA) copolymers containing 3HV monomers by Cupriavidus necator H16. Among various mixtures of plant oils and 3HV-precursors, the mixture of palm kernel oil and sodium propionate was suitable for the biosynthesis of high concentration of PHA (6.8 g L-1) containing 7 mol% of 3HV. The 3HV monomer composition can be regulated in the range of 0-23 mol% by changing culture parameters such as the initial pH, and the nitrogen source and its concentration. PHA copolymers with high weight-average molecular weights (M.) ranging from 1,400,000 to 3, 100,000 Da were successfully produced from mixtures of plant oils and 3HV-precursors. The mixture of plant oils and sodium propionate resulted in PHA copolymers with higher M-w compared to the mixture of plant oils and sodium valerate. DSC analysis on the PHA containing 3HV monomers showed the presence of two distinct melting temperature (T-m), which indicated that the PHA synthesized might be a blend of P(3HB) and P(3HB-co-3HV). Sodium propionate appears to be the better precursor of 3HV than sodium valerate. (C) 2008 Elsevier Ltd. All rights reserved.