Hydrocarbon accumulations are in a quasi-equilibrated condition representing a balance between two main forces that operate in opposite directions: (i) the buoyancy force and (ii) the capillary entry pressure. The buoyancy force is closely tied to the column height and the gravity of petroleum. Heavy, less buoyant oils are often generated during earliest stages of source rock transformation and tend to accumulate in proximity to active kitchens. In contrast, light oils are expelled during the latest stages of source rock transformation and can migrate long distances due to their higher buoyancy. The capillary entry pressure is related to the size of the smallest pore throat and can be modified due to structural processes at any time during the evolution of the associated petroleum systems. Hydrocarbon accumulations may be lost due to trap modifications or become destroyed due to secondary alteration processes (e.g., biodegradation, water washing, and thermal cracking). Both of these processes are controlled by geohistory evolution of the traps in the sedimentary basins.