Response surface analysis was conducted to optimize the concentrations of Tapis crude oil and duration of incubation in
order to achieve optimal microbial growth and crude oil biodegradation. Central Composite Rotatable Design (CCRD)
was employed, where the design contained 13 experimental runs with different combinations of incubation time and
crude oil concentration. The cultures containing mineral salt medium (MSM) with varying crude oil concentrations were
incubated at 30°C, pH6.5 with 150 rpm agitation for 120-336 h. The inoculum contained a consortium of previously
identified as oil degrading bacteria and fungi, namely Pseudomonas aeruginosa UKMP-14T, Acinetobacter baumannii
UKMP-12T and Trichoderma sp. UKMP-1M and UKMP-2M. The analysis showed the duration of incubation plays a significant
role (p<0.05) in affecting the bacterial growth and percentage of total petroleum hydrocarbon (TPH) biodegradation,
meanwhile concentrations of Tapis crude oil has insignificant effect on the responses. Interaction of the two variables was
found to be significant in affecting all the three responses, namely bacterial population, fungal biomass and percentage
of TPH biodegradation. It was predicted through the CCRD that the percentage of biodegradation can be optimized to
reach 86% on the 270th h when 5% (v/v) crude oil was used. This predicted value was verified to be achievable and
reproducible through validation experiments.