A computerized, expert system (FLEX) has been developed that will assess the chemical resistance of flexible membrane liners (FML) used at waste management facilities. These FML's must be chemically resistant to the waste, its leachates, or both. To demonstrate chemical resistancy, the United States Environmental Protection Agency (USEPA) requires the use of Method 9090, wherein the physical properties of the FML are evaluated after various exposure times. After the Method 9090 data are assembled, a reviewer is then responsible for assessing the data and reaching a conclusion about the probability that a proposed FML material will be resistant to the waste/leachate. Knowledgeable judgments as to the chemical resistance of FML require a multitude of considerations. Because such knowledge is not generally available within the USEPA, a computerized, expert system was sought to provide guidance in the review of Method 9090 data. The liner materials of interest were high-density polyethylene (HDPE), polyvinyl chloride (PVC), and chlorosulfonated polyethylene (CSPE).