The Petroleum Data System, a collection of general field and reservoir information, has been available for public use for approximately 3 years. Data have been used in a variety of studies by oil companies, consultants, and government agencies. In particular, many studies have been done in an effort to determine the potential of specific basins for future exploration and drilling, the feasibility of certain types of enhanced recovery techniques, and future reserves from existing fields. The different types of output are histograms, scatterplots, bargraphs, correlations, simple listings, and summary reports obtained by manipulation of the data in the file. These examples illustrate problems that have to be faced in working with large data bases, such as

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missing data, conflicting data, and fuzzy or nonstandard data definitions.

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