Hydrocarbon microseepage generally refers to the rapid vertical migration of the hydrocarbons from subsurface reservoirs to the earth's surface. The migration rate is relatively fast, but not in quantities large enough to measurably deplete a reservoir in geological time. The use of the geochemical data at the surface for oil and gas exploration is dependent on data collection, data processing, and interpretation. Near-surface geochemistry gives no information about reservoir depth, thickness or permeability, but is able to define spatially the size, shape and location of petroleum reserves.