Despite the depleting fossil fuel reserves and growing environmental concerns, the world’s energy consumption is still rising, resulting in the development of unconventional and alternative energy sources. A byproduct from the distillation of crude oil, residual fuel oil (RFO), also known as bunker fuel, finds extensive application in power generation and marine transportation. Because of its high viscosity, high Sulphur content and incomplete combustion, RFO has not gotten much attention in recent fuel research, despite its high energy content and widespread availability. This study examines RFO's physicochemical and thermal properties in contrast with standard fuels such as diesel, biodiesel and high-sulfur fuel oil. In determining RFO's suitability for combustion applications, a comprehensive laboratory investigation was performed, including viscosity, density, calorific value, cetane number, Sulphur content, and auto-ignition temperature tests. Thermal degradation patterns, combustion temperature ranges, and emission properties were also investigated. The results conclude that RFO needs to be pretreated before use, with options like heating or blending. The calorific value of RFO is found to be close to diesel, making it a potential substitute for an alternative fuel, a viable and cheaper option, for stationery and large-scale engines. There are still certain issues related to its use, such as ignition delays, particulate emissions and regulatory compliance. The study suggests that RFO has the potential to be used as fuel, when suitably modified, in areas where getting access to refined fuel is difficult. Future work on the study includes fuel upgrades, engine system modifications & long-term combustion and emission studies to improve its usability and acceptability.