As per IEC Standards, partial discharge (PD) are “localized electrical discharges that only partially bridge the insulation between conductors.” PD is local electrical stress on the insulation it can be internal or on the surface of the insulation. Petroleum-based mineral oil is traditionally used as insulation for power and distribution transformers over the century because of its scientifically proven advantages. But the use of mineral oil has disadvantages to the environment also PD effect significantly deteriorates insulation strength and can cause the transformer to fail. The ester-based Synthetic oil is been used as an alternative to mineral oil in recent decades due to its biodegradable and fire-resistant properties. In this paper, the partial discharge effect of mineral oil and synthetic ester oil is investigated experimentally as per IEC Standards and Phase Resolved Partial Discharge analyses are carried. The phase vs Charge, Charge vs Number of counts, and Phase vs Number of counts patterns are obtained individually for both oils, and results are compared and presented for PD deterioration effects.