Acoustic reflectometry has been shown to be an effective technique for detecting defects, such as holes and blockages, in relatively short, single lengths of pipe. This paper discusses briefly the physical basis of the technique and then describes the results of a series of experiments that were designed to evaluate the suitability of using this approach for monitoring the health of natural gas pipelines. Such pipelines will typically be many kilometres long, have diameters of up to 1 m and may form part of a complex network of pipelines. Previous studies have demonstrated that acoustic reflectometry techniques can be used to detect pipeline defects in relatively small bore pipelines with lengths of several hundred meters. The results reported in this paper indicate that even when using fairly crude equipment, the technique can be successfully applied to detect defects in single pipelines and pipeline networks with large diameters and lengths exceeding 5 km. Although the results presented in this paper are not conclusive, they do provide the necessary justification for a second phase of experiments to be conducted to extend the scope of the technique further.