The gas industry has an excellent safety record in operating high pressure transmission pipelines. Nevertheless, it is important that pipeline operators have an understanding of the possible consequences of an accidental gas release, which may ignite, in order to help manage the risks involved. This paper describes two full scale experiments, conducted as part of a research programme into the consequences of pipeline failures, undertaken by an international collaboration of gas companies. The experiments involved the deliberate rupture of a 76km length of 914mm diameter natural gas pipeline operating at a pressure of 60 bar, with the released gas ignited immediately following the failure. Instrumentation was deployed to take detailed measurements, which included the weather conditions, the gas outflow, the size and shape of the resulting fire, and the thermal radiation levels. The results provide important data for the validation of mathematical models, used in developing risk assessment methodologies, and in establishing those standards and design codes for gas pipelines that are risk based.