The generation of one or more three-dimensional (3-D), freehand drawings, based on integrated analysis of a two-dimensional (2-D) geologic database (e.g., borehole data, seismic profiles, surface geology, etc.), is proposed here as a rewarding exercise in the development of a final interpretation of subsurface geologic structures. A freehand 3-D drawing based on integration of 2-D interpretive structural contour maps (of at least two horizons) and structural cross sections can clarify and verify the 3-D details of complex subsurface geologic structures, check on the internal consistency of the interpretation, uncover untenable, interpretive, geologic configurations, and highlight possible obscure trap geometries. In some cases freehand 3-D drawings can aid in the visualization of impenetrable 3-D images produced by computer software programs. Isometric projection or linear perspective drawings are generally the most useful kinds of 3-D renditions, but strict adherence to these disciplines is not a requirement in the generation of an initial 3-D sketch. Generating a 3-D image using computer software is dominantly the functional domain of the left hemisphere of the brain (left brain), whereas the generation of freehand 3-D drawings is dominantly the functional domain of the right brain and requires penetrative visualization in the conversion of 2-D data to 3-D imagery. The right brain excels in intuitive, creative, imaginative structural interpretation. Examples of freehand 3-D drawings of complex subsurface and surface geologic structures, both self-generated and from literature, are presented along with some auxiliary 3-D analog modeling methods.