The simulation of realistic multiphase flow problems in petroleum reservoirs requires means for handling the complicated structure of the reservoirs such as complex boundaries, faults, fractures, and horizontal wells. A numerical reservoir simulator has recently been developed to be able to handle these features for a wide range of applications. This fully implicit simulator is based on a three-dimensional, three-phase black oil model. It can also be used to solve a dual-porosity, dual-permeability black oil model in a fractured reservoir. The space discretization method used in this simulator is based on a block-centered finite difference method with harmonic averaged coefficients (equivalently, a mixed finite element method). In this paper we report an application of this simulator to a problem involving injection and production from horizontal wells in a reservoir where a coning tendency is important, and present a benchmark comparison with other simulators by fourteen petroleum organizations.