In 1982 Esso Australia completed a fundamental re-assessment of the undiscovered oil and gas potential of Australia. In the seven years since Esso's previous major study there has been a marked upsurge in exploration for hydrocarbons, particularly oil. During this period several hundred wells have been drilled and hundreds of thousands of kilometres of seismic data have been recorded. New discoveries of both oil and gas have been made in several areas. Because of this influx of new data, a re-assessment was considered timely. The assessment utilised computer-based techniques and incorporated improvements in assessment and risk theory. The study involved the identification of more than one hundred individual plays followed by the volumetric and risk assessment of those plays. The risked assessments of the individual plays were then combined to produce an overall assessment for Australia in the form of cumulative probability distributions for oil and gas. The results show that the potential exists in Australia to find a significant volume of additional oil, possibly equivalent to the amount of oil discovered to date. The assessment also indicates a high probability of abundant undiscovered gas. Although the perceived resource base is quite encouraging, no consideration was given in the assessment to operational, economic or political constraints. Consequently there is no discovery time-frame implied within the assessment results. The rate of discovery will be determined by the amount and quality of exploration effort, which in turn will be dictated by the economic and political environment under which industry is allowed to operate.