Damage from a force outside the pipeline is the primary cause of natural-gas pipeline service failures in the U.S. The second and third main causes of line service failures are material failure and corrosion. These are the major conclusions of an analysis of reports of line service incidents filed with the U.S. Department and Transportation (DOT). The study, covering incident reports for a recent 14-year period, analyzed reportable incidents from the DOT's Office of Pipeline Safety Regulation OPSR) 20-day incident report forms to assess the causes of incidents and the safety record of the industry. The data used for the analysis were collected from 1970 through June 1984 by DOT-OPSR. In June 1984, changes in the report format reduced the amount of data collected. Therefore, 1984 data reported here represent only the first half of that year