In this U.S. Energy Research and Development Administration (ERDA) investigation a revised version of a three-dimensional finite-difference diffusivity model is presented with the capability of simulating horizontal or vertical induced fractures by several different methods. Fractures may be of finite, semi-infinite, or infinite flow capacity. In the first case, the fracture width and permeability is specified and the appropriate permeability of each node penetrated by a fracture is altered according to the relationship for linear beds in parallel. In addition, the block size normal to the fracture orientation is decreased to a very small value thus giving a reasonable representation of the fissure. A semi-infinite fracture is simulated for a specified total rate by uniformly distributing the flow along the reservoir nodes penetrated by the fracture. Finally, an infinite capacity fracture may be simulated for either the constant potential or constant rate case. In addition to simulating gas, liquid, or heat flow in a heterogeneous, anisotropic fractured media this model (1) relates block pressures to wellbore pressures through radial flow equations, (2) is unlimited in the number of time-steps per run, (3) offers three different implicit solution algorithms, (4) will simulate pressure (temperature) or rate pulse tests, (5) accumulates elapsed time, total production, and material balance errors, (6) can begin each run with any pressure distribution in one of two different formats, and (7) can be used with a mixture of hydrocarbon gases containing up to 14 components over reduced temperature and pressure ranges of 1.1 to 3.0 and 1.1 to 20.0, respectively. The generality of the model developed precludes listing the entire scope of its applications. Sample problems are given for the cases of liquid flow and heat conduction. Also a special 3-D fracture problem is included which shows the usefulness of this package to the natural gas industry.