Flat plate oscillating heat pipe (FP-OHP) is a unique heat transfer device and considered as a promising candidate for effective heat transfer device in electronics industries. A number of theoretical studies and experimental investigations have been carried out on FP-OHP in the past decades after its invention. However, due to the operational characteristics of FP-OHP, the effect of various parameters on the thermal performance of FP-OHP has not been completely revealed so far. This paper attempts to discuss the effect of operational parameters on the thermal performance of FP-OHP. In this study, the FP-OHP was investigated with different charge ratios, orientations, working fluids, and heat loads from 10 W to 150 W. In order to investigate the effect, 18 parallel square channels of 2 × 2 mm2 are machined onto pure copper plate (93 × 70 × 8 mm3) to form FP-OHP. DI water, ethanol, methanol, acetone, and FC-72 are investigated. The measured thermal resistance was strongly dependent on operational parameters. The optimum performance was observed with acetone with a charge ratio of 70% in the vertical orientation. The lowest thermal resistance of 0.39 °C/W is achieved using acetone as a working fluid at 100 W. A Kutateladze number (Ku) was used to compare the experimental data and found to be suitable for prediction of the thermal performance of FP-OHP with standard deviation of 15%.