Two low structured mathematical models for fed-batch production of polyhydroxybutyrate and poly[hydroxybutyrate-co-hydroxyvalerate] by Cupriavidus necator DSM 545 on renewable substrates (glycerol and fatty acid methyl esters-FAME) combined with glucose and valeric acid, were established. The models were used for development/optimization of feeding strategies of carbon and nitrogen sources concerning PHA content and polymer/copolymer composition. Glycerol/glucose fermentation featured a max. specific growth rate of 0.171 h(-1), a max. specific production rate of 0.038 h(-1) and a PHB content of 64.5%, whereas the FAME/valeric acid fermentation resulted in a max. specific growth rate of 0.046 h(-1), a max. specific production rate of 0.07 h(-1) and 63.6% PHBV content with 4.3% of 3-hydroxyvalerate (3HV) in PHBV. A strong inhibition of glycerol consumption by glucose was confirmed (inhibition constant k(i,G) = 4.28 x 10(-4) g L-1). Applied concentration of FAME (10-12 g L-1) positively influenced on PHBV synthesis. HV/PHBV ratio depends on applied VA concentration. (C) 2013 Elsevier Ltd. All rights reserved.