A Decision Support System is a class of computer software with information, databases, and computer models integrated together to help people solve broad, semi- structured problems. Ground water contaminant transport modeling is an example of this type of problem, and a new decision support system, OASIS, was developed to make ground water modeling easier and more accessible. The system contains a ground water biodegradation model, model documentation, background information, data from chemical and hydrogeologic databases, and data management tools. The system was developed using HyperCard software on a Macintosh personal computer. It currently has over 1600 different computer screens of information and occupies approximately 10 megabytes of hard disk storage. OASIS is the product of four software technologies. Graphical interfaces allow a more intuitive and effective form of communication with the computer compared to text-based interfaces. Concepts from the field of Hypertext were applied to design the extensive electronic documentation and databases. An Expert Systems approach was used to incorporate the decision process a practicing biorestoration expert uses to clean up waste sites. Finally, Object Oriented Programming permitted scientists with little programming experience to develop OASIS by manipulating preexisting software objects rather than writing computer code, greatly increasing the productivity of the project team. One unique decision support tool in the system is the hydrogeologic database (HGDB). The data was obtained from a national survey of hydrogeologists and was organized by adapting an existing graphical aquifer classification system. Raw data, summary statistics, and the aquifer classification system were incorporated into the decision support framework to create a software tool for estimating hydrogeologic parameters. OASIS is a new type of modeling software where ground water models, data, and knowledge are integrated together using a graphical interface and an easily modified software architecture. Two groups of users can benefit from the system: current modelers who needs more efficient interfaces and data management tools, and people who are not using models now because the modeling process is too involved and needs specialized knowledge.