• AC breakdown strength of coconut oil is studied as against commercial soybean oil. • Analyzed the effect of aging (120 °C, 2 weeks) and mineral oil on AC breakdown strength. • AC breakdown data are statistically analyzed using Normal and Weibull distributions. • Aging or mineral oil reduces the withstand voltage, but the effect is less intense in coconut oil. • Coconut oil can be a potential replacement for traditional mineral oils. The effect of residual mineral oil on the AC breakdown strength of vegetable oil is widely studied to understand vegetable oil's reliability and dielectric integrity in retro-fitting a mineral oil-filled transformer. This paper describes the analysis of experimental results on two types of vegetable oil, namely –refined, bleached, and deodorized (RBD) coconut oil and commercial vegetable oil (MIDEL eN1215) derived from soybean oil seeds. The latter is also to act as a benchmark in analyzing the breakdown performance of RBD coconut oil, which is recently studied as a potential alternative to replace mineral oil from transformers located in tropical countries. The AC breakdown voltage tests were conducted using ASTM D1816 method at normal ambient conditions for both fresh and aged oils and considering 10 and 30% mineral oil in these vegetable oils. It is found that the distributions of breakdown voltages in RBD coconut oil, especially the lowest AC breakdown voltage, are similar to those of commercial vegetable oil for transformers. Therefore, from the viewpoint of AC withstand voltage, RBD coconut oil is equivalent to commercial vegetable oil under new conditions and even better under aged conditions or when mixed with mineral oil.