This paper presents an assessment evaluation of methane gas yield using a derived model based on the hydraulic retention time (HRT) of the feed stock (waste fruits) undergoing biotreatment in the digester. The derived model; γ = e (3.5436 α + 2.0259) indicates an exponential relationship between methane yield and the HRT. Statistical analysis of the model-predicted and experimental gas methane yield for each value of HRT considered shows a standard error of 0.0081 and 0.0114% respectively. Furthermore, the correlation between methane yield and HRT as obtained from derived model and experimental results were evaluated as 0.9716 and 0.9709 respectively. Methane gas yield per unit HRT as obtained from derived model and experiment are 0.0196 and 0.0235 (m 3 ·kg −1 VS) days −1 respectively. Deviational analysis indicates that the maximum deviation of the model-predicted methane yield from the corresponding experimental value is less than 16%. It was also found that the validity of the model is rooted on the expression 0.2822 ln γ = α + 0.5717 where both sides of the expression are correspondingly approximately equal.