Publisher Summary The structural work done in the oilfield aims at producing the best possible picture of the three-dimensional geometry of the complex of more or less deformed rocks through which the wells of the field have been drilled. Thorough and comprehensive operation is carried out to make the best possible and most reliable description of the shape of the reservoir or reservoirs in the field, because that is where the interest of the industry lies. At the very least, a contour map showing as accurately as possible the depth of the top of each reservoir zone is required for use in operational matters as selecting well locations or targets and estimating reserves. If the tectonic situation is at all complex, it is likely that other maps will be needed—that is, maps on the tops of reservoir subzones; on the base of the reservoir zone, if its thickness is variable; perhaps isochore maps of such units; all the maps of course showing the positions of faults that might act as barriers within the reservoir. It is up to the production geologist to decide which documents to prepare in view of the peculiarities of the case he/she is dealing with.