This study investigated the biodegradation of Tapis light crude petroleum oil (TLCO) in coastal seawater samples utilising palm oil mill effluent final discharge (POME FD) as biostimulant using rotatable central composite design (CCD) under response surface methodology (RSM). In a 23-day study, the independent variables (factors) were initial TLCO concentration, POME FD dosage, and incubation time, and the dependent variable (response) was TLCO biodegradation. The residual TLCO analysis was carried out using the gravimetric method, which was then verified by GCFID. The gravimetric analysis produced a coefficient of determination (R2 = 0.9764) and a probability value (P < 0.0002) indicating significance for the regression model. Similarly, the GCFID analysis identified a coefficient of determination (R2 = 0.9973) and a probability value (P < 0.0001) indicating significance for the regression model. Numerical optimization based on the desirability function was performed, gravimetric and GCFID analyses revealed errors of 4.81 and 1.04, respectively. © 2022 The Authors