Ports are generally classified according to the type of traffic they handle. Based on the nature of cargo, ports can be industrial, commercial, or comprehensive. Industrial ports specialize in bulk cargo such as grain, sugar, ore, oil, and chemicals, facilitating large-scale industrial trade. Commercial ports, on the other hand, primarily handle general cargo, including packaged products and manufactured goods, and often accommodate passenger traffic as well. Comprehensive ports, among the most significant globally, manage both bulk and general cargo in large volumes, making them essential trade hubs. Another way to classify ports is based on their location. Inland ports are situated away from the coastline and connect to the sea through rivers or canals. These ports typically accommodate flat-bottom ships or barges. Examples include Manchester, connected via a canal, and Memphis, located on the Mississippi River. Other notable inland ports are Mannheim and Duisburg on the Rhine, and Kolkata on the Hooghly River, a branch of the Ganga. In contrast, out ports are deep-water ports constructed away from main ports to handle larger vessels that cannot dock at the primary port. A classic example is the Athens-Piraeus combination in Greece, where Piraeus serves as the out port for Athens. Ports are also categorized based on specialized functions. Oil ports focus on the processing and shipping of oil, further classified into tanker ports and refinery ports. Examples include Maracaibo in Venezuela, Es Sukhairah in Tunisia, and Tripoli in Lebanon as tanker ports, while Abadan in the Gulf of Persia functions as a refinery port. Ports of call originally emerged as stopping points for refueling and resupplying ships along major sea routes, later evolving into commercial ports—Singapore, Aden, and Honolulu exemplify this category.