Gas and oil migrate from the site of thermal generation to the site of final entrapment. The direction of this migration is controlled by the basin geometry in existence during the time of migration, while the length of the migration path is controlled by the available permeability of void channels or natural fractures. Gas and oil generally migrate in directions normal to the regional pressure contours, thus normal to regional structural contours. Focusing of migration paths results from certain favorable geometric parameters connected with basin configurations. Major migration paths, and hence preferred areas of hydrocarbon entrapment, are predictable to a large degree. Migration focusing is not a theoretical concept but rather a valid explanation of numerous observatio s is most basins of the world. Examples are given from such different geologic settins as the Middle Magdalena basin and Lower Magdalena basin, Colombia (oil), northwest Germany (gas), and the Gippsland basin, Australia (gas and oil).

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