This study assessed environmental and biological factors influencing oil palm fruit set and yield decline. This study was conducted in Malaysia, Teluk Intan, Perak State, at the Malaysian Palm Oil Board (MPOB) Research Station during February 2019 to January 2020. The optimal oil palm fruit set is continuously declining, attributed to genetic origins, inflorescence sex ratio, pollinator insect (Elaeidobius kamerunicus Faust) and environmental factors (rainfall, field temperature, wind velocity, evaporation rate and sunshine duration). This study was conducted to investigate the most influential factor responsible for the decline in oil palm fruit set. The analysed results showed that oil to bunch was the highest contributor to oil yield, followed by mesocarp to fruit and fresh fruit bunch. The novelty of this study as a unique contribution to the oil palm industry primarily identified E. kamerunicus as the most influential biological factor in fruit set success, followed by wind velocity and field temperature, especially in older or taller palms with reduced male inflorescence. These findings can be used to develop strategies to combat declining oil palm fruit setting and low oil yield.