<p>Ionic liquids (ILs) are new materials with unique chemical and physical properties, including high-temperature stability, low vapor pressure, and a high ability to dissolve other substances. ILs are ideal for various industrial applications due to their properties, including extraction, catalysis, and desulfurization. This article review discusses the density, viscosity, melting point, and polarity of ionic liquids (ILs), as well as how these properties influence their effectiveness in processes such as liquid–liquid extraction for the separation of aliphatic hydrocarbons, aromatics, deep desulfurization, and heavy metal removal. In addition, it discussed the benefits of ILs in oil processing, including improved selection, reduced environmental impact, and lower energy use, while also addressing concerns such as cost and security. The study demonstrates that ionic liquids (ILs) can serve as alternatives to traditional solvents, addressing industry issues in a more environmentally friendly and effective manner.</p>