We have designed a fast parallel simulator that solves the acoustic wave equation on a GPU cluster. Solving the acoustic wave equation in an oil exploration industrial context aims at speeding up seismic modeling and Reverse Time Migration. We use a finite difference approach on a regular mesh, in both 2D and 3D cases. The acoustic wave equation is solved in either a constant density or a variable density domain. We use CUDA to take advantage of the GPUs computational power. We study different implementations and their impact on the application performance. We obtain a speedup of 11 for Reverse Time Migration and up to 30 for the modeling application over a sequential code running on general purpose CPU.