The reliance on flexible membrane liners (FML) has arisen because they are impermeable to a variety of waste chemicals and they are easily produced at reasonable cost. Unfortunately, their long-term field performance remains to be proven. A multitude of design, construction, and operational factors has been identified as having greater or less potential for interfering with FML performance. Many of these factors can cause liner failure (leakage more than a specified amount). All of the factors must be recognized and their probability of occurrence and degree of performance interference estimated. From this information, a reliability prediction model can be constructed. As data on design, construction, operation, and actual performance of land disposal systems accumulate, the model can then be verified and refined. The FML model will be integrated with similar analyses of other system components into an overall land disposal system reliability prediction model.