In petroleum geology, a trap is defined as a geometrical arrangement of rocks that allows accumulation of hydrocarbons in the subsurface. A suitable trap is made up of two important elements including the reservoir rock and the seal rock. The reservoir rock, regardless of its lithology and poro-perm properties, provides the storage space for hydrocarbons. In contrast, the seal rock prohibits the hydrocarbons from escaping the reservoir rock. Sandstones and carbonates usually provide the best petroleum reservoir rocks, while evaporites and shales create efficient seal rocks in most petroleum systems. The physico-chemical properties of hydrocarbons accumulated in the reservoir rock (i.e., the API gravity and the gas-liquid ratio) are predominantly controlled by two factors: (i) the organofacies of the related source rock and (ii) the characteristics of the associated trap. Traps can receive charges from multiple kitchens or spill/leak some of their hydrocarbons into nearby traps. Analyzing trap charge dynamics is possible through multi-dimensional modeling studies in combination with comprehensive geochemical analysis of reservoir fluids.