Power transformers are critical components in electrical transmission and distribution systems, serving the essential function of stepping up and stepping down voltage levels to ensure the system operates efficiently and reliably. Traditionally, mineral oil has been widely used as the insulating and cooling medium due to its ease of application and low viscosity. However, mineral oil presents significant limitations in terms of safety and environmental impact, such as its low flash point, which increases fire risk, and its poor biodegradability.As an alternative, ester-based insulating oils—both natural esters (NE) and synthetic esters (SE)—offer several advantages, including higher flash and fire points, as well as excellent biodegradability. These characteristics make ester fluids particularly suitable for transformers located in sensitive environments, such as residential areas, public facilities, and conservation zones. Nevertheless, the widespread adoption of ester-based insulating oils still requires a solid technical and policy framework to support their implementation. This research is conducted as a literature review aimed at examining international acceptance standards for ester fluids, analyzing their advantages and limitations compared to mineral oil, and assessing the operational characteristics and maintenance requirements of power transformers utilizing ester insulation. The data were gathered from international standards, scientific publications, industry reports, and informal interviews with stakeholders in the power sector and academic experts. The findings indicate that ester fluids possess significant safety advantages, with flash points exceeding 250°C and fire points over 300°C, far surpassing mineral oil, which typically has a flash point of around 135°C. This greatly enhances transformer safety by reducing fire risks. Moreover, ester fluids with moisture content below 200 ppm can maintain superior dielectric strength compared to mineral oil with moisture levels as low as 30 ppm, thereby slowing down the aging process of the insulation system. Ester oils also demonstrate higher breakdown voltages, with values exceeding 45 kV for a 2.5 mm electrode gap, compared to approximately 30 kV for mineral oil. In terms of pour point, NE shows a relatively high pour point of around -10°C, while SE and MO have lower pour points of -45°C and -40°C, respectively. This limits NE's application in extreme cold environments, though it is irrelevant for tropical countries like Indonesia. However, ester fluids have higher viscosity values (below 50 cSt) compared to mineral oil (below 12 cSt), which may reduce heat dissipation efficiency during transformer operation. Additionally, NE is more prone to oxidation, requiring proper storage and handling procedures to maintain its quality. From an environmental perspective, both NE and SE significantly outperform mineral oil, with biodegradability levels of 97% and 80%, respectively, compared to only 30% for mineral oil. This makes ester fluids a far more sustainable choice, minimizing the risk of environmental contamination and reducing cleanup costs in the event of leaks. The outcomes of this study are expected to contribute to the development of national standards for ester-based power transformers in Indonesia, supporting the broader strategy of implementing green transformer technology. This initiative not only aims to enhance operational efficiency and reliability but also aligns with Indonesia's commitment to transitioning towards sustainable energy and achieving its net-zero emissions target.