Since independence in India there has always been shortage of electricity and at no point of time we have been able to meet the peak demand. The gap between the demand and generation can be minimized by either improving the installed capacity or reducing the consumer demand. The gap between availability & demand is of order 6% as on date. If we take into account the issues like environment pollution and global warming, the preferred option is to increase the energy efficiency or minimize the consumer demand, as in the other alternative particularly in India where thermal generation dominates increased environmental pollution is inevitable. The problem of using the new environmentally friendly insulating liquids like synthetic and natural esters for power transformers is presented in this article. The positive and negative properties of the esters are described on the basis of a comparison with the most popular insulating liquid like mineral oil. The results of the experimental studies were taken into account as well as the results of works presented in the world literature. Conclusions from the analysis will indicate that the wide knowledge about ester properties is necessary to correct design process and to proper exploitation of the power transformers filled in esters.