This paper presents electromagnetic interference effects of transmission lines upon nearby gas pipelines and determines the mitigation requirement in order to reduce the induced voltage on the pipelines to acceptable limits during steady state and fault conditions. The mitigation system has been designed and simulated for a typical gas pipeline located in shared right-of-way with HV power lines using CDEGS software. The design model was based on the induced voltage profile of the gas pipelines. Gradient control wire are considered as a mitigation system. The gradient wire considered consists of one or more bar zinc conductors buried parallel and near to the pipeline and repeatedly connected to it. A set of graphs has been produced to illustrate the effect of changing the length of mitigation wires on the induced pipeline voltage.