This study presents a comparative analysis of Partial Discharge (PD) detection and localisation in Mineral Oil (MO) and Refined, Bleached and Deodorised Palm Olein (RBDPO) based on the Ultra-High Frequency (UHF) technique. A PD experiment was arranged using a needle–plane electrode configuration, and the gap was set to 35 mm. To initiate the PD, the applied voltage was gradually increased from 15 kV to 25 kV in 5 kV/step. In total, 4 patch-type UHF sensors were mounted externally on the steel tank wall at predetermined locations to capture the PD signals. An electrical PD event was detected simultaneously using an Impedance Matching Circuit (IMC). The UHF PD signals were denoised by a Gaussian filtering method. The Time Difference of Arrival (TDOA) was then determined through the First Peak Method (FPM) and Cumulative Energy Method (CEM). PD localisation was carried out based on the TDOAs obtained from both FPM and CEM. It is found that although RBDPO exhibits higher attenuation of UHF PD signals, it achieves lower localisation error as compared to MO. Performance assessment further confirms that PD localisation is better in RBDPO than in MO.