Petroleum resource assessment begins with geological study of sedimentary basins and subdivision of the sedimentary sequence and petroleum prospects into plays. Next, information about the plays, the area and geometry of their traps, and the sizes of their accumulations are compiled in a database within the AUSTPLAY program. Some data are sorted, plotted, and analyzed by the program. All data are examined by specialist geoscientists, who interpret the historic trends, select analogues, make quantitative models, and use subjective judgment to determine the information to be used in the assessment.