This paper reports on a comparative study of statistical Breakdown Voltage (BDV) in a natural ester oil namely jatropha curcas methyl ester oil (JMEO) extracted from the fruit seeds of jatropha curcas plants, mineral oil (MO) and two JMEO/MO oil mixtures (namely (50%JMEO+50%MO) and (80%JMEO+20%MO)) using spherical electrode under DC and AC voltages. It is shown that the average AC breakdown voltage of JMEO is higher than that of mineral oil. Meanwhile it is similar under DC voltage. The statistical analysis shows that all large data groups (n>40) for AC and DC breakdown voltages of JMEO, MO and oil mixtures obey to the normal distribution law. This is proved using Shapiro-Wilk test, skewness and kurtosis values. It also observed that AC mean breakdown voltage of JMEO is higher than that of oils mixture (50%JMEO+50%MO) and MO, but it is similar with oils mixture (80%JMEO+20%MO). AC mean breakdown voltage of MO is the lowest one. DC mean breakdown voltages of JMEO, MO and oil mixtures (50%JMEO+50%MO) are similar. In contrast, DC mean breakdown voltage of oils mixture (80%JMEO+20%MO) is the highest one.