Pipelines represent the most important mode of transportation for petroleum products, and therefore for energy, in the developed world. The pipeline infrastructure and the volume of products transported have continued to grow as demand for energy has increased. At the same time, the pipeline infrastructure system has continued to age. This increased demand for energy combined with the expansion of cities and suburban areas will require the aging pipeline infrastructure not only to expand but to reliably and safely deliver energy services in support of a nation's economy. Although many countries have well-developed systems for protecting the public and environment from dangers of oil and gas pipeline failures, there is always the chance that a pipeline can leak, ultimately leading to environmental and economic catastrophe if left unrepaired. To prevent circumstances potentially hazardous to people and the environment, leak detection is a critical part of pipeline operation. Consequently, incorporation of a leak detection system into the pipeline integrity management plan is a requirement of both the Gas and Liquids "Rules" issued by the US Department of Transportation (USDOT). Small leaks are very difficult to identify at the source and are a major safety concern. Early detection of leaks can greatly reduce the loss of product from the pipeline and avoid or minimize "environmental" damages. This paper describes the development and testing of an innovative free-swimming acoustic method for detecting minor leaks in pipelines. Several case studies demonstrate the effectiveness of such a technology.