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 consider 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. All the computations are done in single precision, since double precision is not required in our context. 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 speed up of 10 for Reverse Time Migration and up to 30 for the modeling application over a sequential code running on general purpose CPU.