The operational efficiency and longevity of oil-type power transformers are mainly dependent on the insulating and cooling properties of the transformer oil used. Synthetic ester (MIDEL 7131 OIL) and mineral oil (Shell Diala S4 ZX-I) are commonly employed in transformers due to their distinct chemical compositions and performance attributes. This study aims to assess the impact of the weight of MIDEL 7131 and Shell Diala S4 ZX-I type oils on the overall mass and performance of oil-type power transformers. The research investigates the influence of the oil types on the transformer’s operational performance and its overall weight. The findings contribute to a deeper understanding of how oil selection affects transformer design, with particular emphasis on the implications of oil weight. The results of this study are crucial for advancing transformer oil selection strategies, promoting enhanced energy efficiency, and optimizing the weight of the transformer design for more reliable and efficient transformers.