The determination of the location of a leak in a pipeline. In onshore operations, this can be done by external detection or by using material balance leak-detection systems. In offshore operations, the task is more difficult because of the lack of inlet flow-rate measurements and the considerable solubility of natural gas in seawater at high pressures and low temperatures (seafloor level).

In deepwater operations with multiphase flow, indications of a leak may not be present at the ocean surface or it could be considerably displaced from the site of origination. In these circumstances, an energy-balance technique based on the changes in frictional losses through the pipeline is a powerful tool.