Electroinsulating materials are important and expensive parts of every electrotechnical equipment. One of the most common used electroinsulating materials are electroinsulating oils. In electrotechnical practice, the greatest utilization for mineral oils is due to their great electroinsulating features, simple accessibility and their low price. Opposite to this fact, the environment problematic is getting into spotlight more and more presently. Enterprises that handle the production of power transformers conduct research on mineral oil alternatives, which could be more environment friendly. A possible alternative for the today used earth oil based oils are vegetable oils. It is necessary to know electroinsulating features of the vegetable oils to be able to appreciate the applicability of their utilizing as the alternative for mineral based oils. Due to this fact, this paper deals with research and comparison of electroinsulating features of vegetable, mineral and silicone oils.