A mathematically based fed-batch bioprocess demonstrated the suitability of using a relatively cheap and renewable substrate (butyric acid) for Pseudomonas putida CA-3 high cell density cultivation. Butyric acid fine-tuned addition is critical to extend the fermentation run and avoid oxygen consumption while maximising the biomass volumetric productivity. A conservative submaximal growth rate (μ of 0.25 h(-1)) achieved 71.3 g L(-1) of biomass after 42 h of fed-batch growth. When a more ambitious feed rate was supplied in order to match a μ of 0.35 h(-1), the volumetric productivity was increased to 2.0 g L(-1) h(-1), corresponding to a run of 25 h and 50 g L(-1) of biomass. Both results represent the highest biomass and the best biomass volumetric productivity with butyrate as a sole carbon source. However, medium chain length polyhydroxyalkanoate (mcl-PHA) accumulation with butyrate grown cells is low (4 %). To achieve a higher mcl-PHA volumetric productivity, decanoate was supplied to butyrate grown cells. This strategy resulted in a PHA volumetric productivity of 4.57 g L(-1) h(-1) in the PHA production phase and 1.63 g L(-1) h(-1)over the lifetime of the fermentation, with a maximum mcl-PHA accumulation of 65 % of the cell dry weight.