Engineer Norhan Thamer Assi Petroleum refining (crude oil refining) is a series of complex physical and chemical processes aimed at transforming crude oil extracted from underground reservoirs into high-value products such as liquefied petroleum gas (LPG), gasoline, diesel fuel, jet fuel, and asphalt. The process begins with preliminary treatment to remove water, salts, and sand from the crude oil using electrical desalting units, which protect refinery equipment from corrosion and blockage. The crude oil is then sent to the atmospheric distillation stage, where it is heated to temperatures ranging from 350°C to 400°C and introduced into a distillation column. Its components are separated according to their different boiling points: light gases are collected at the top of the column, followed by naphtha and gasoline, then kerosene and jet fuel, and finally diesel, while the heavier residues remain at the bottom. To utilize these heavy residues, they are transferred to a vacuum distillation unit operating under reduced pressure, which allows the separation of heavy hydrocarbons at lower temperatures without causing thermal cracking or coking. This process produces lubricating oils, waxes, and asphalt. The next stage involves chemical conversion processes such as catalytic cracking, which breaks heavy hydrocarbon molecules into lighter and more valuable products, catalytic reforming, which improves gasoline quality by increasing its octane number, and alkylation, which combines smaller molecules to produce high-quality fuel components. Subsequently, hydrotreating is carried out to remove sulfur, nitrogen, and other impurities from petroleum products by reacting them with hydrogen in the presence of catalysts. This step significantly reduces harmful emissions and enhances fuel quality. In the final stage, different petroleum streams are blended in carefully controlled proportions with specific chemical additives to meet commercial and regulatory specifications, such as Gasoline 91 and Gasoline 95. The finished products are then stored in large tanks before being distributed to markets. Through these integrated refining processes, crude oil is transformed from a complex raw material into a wide range of essential products that support transportation, industry, and energy sectors worldwide.