Natural fractures of one type or another are typical of hydrocarbon reservoirs in virtually all structural settings, from tightly folded strata to otherwise undeformed, flat lying formations. However, since different structures impose fracture-forming stresses onto the strata in different ways, significantly different fracture intensities and patterns may be produced in different settings. Moreover, not all fractures of a given set are equal in length, aperture, or height (and therefore in their effect on permeability or seismic signal), even if they formed in the same stress regime: The range of apertures or lengths within a fracture set, for example, may consist of numerous narrow and/or short fractures and a few wide, long ones. This paper briefly discusses "regional" fractures, fractures that are common as relatively regular, extensive, parallel to subparallel features over wide areas within relatively undeformed strata (Figure 1).