This paper presents the integrated deterministic/probabilistic approach to petroleum resources definitions, classification, determination and reporting. The definitions being proposed herein are consistent with, but more complete than the recently published SPE/WPC revised definitions and encompass the full range of resources inventory to meet the diverse customers' needs. The petroleum definitions and classification guidelines developed follow closely those of the SPE (1987), but are generally a synthesis of approved working and new proposed revised definitions from SPE, SPEE, Petroleum Society of Canadian institute of Mining (CIM), World Petroleum Congress (WPC), multi-national oil companies operating in the country, the Securities and Exchange Commission (SEC) and published sources in technical journals. The proposed classification covers the total resources inventory i.e. Discovered and Undiscovered resources. For the estimated recoverable petroleum, key broad categories used are Ultimate Recovery, Potential Recovery and Speculative Recovery to meet both the nation's and multi-national oil company needs and requirements. The last two categories which are not captured in the SPE/WPC draft revised classification are of special importance for applications of planning which range from block promotion and developing new investment to arrangement in exploration and development. The integrated assessment methodology proposed herein is flexible as it provides a mechanism for reconciliation and summation of resources between deterministic and probabilistic methods. Expectation or Expected Value (EV) which can be derived probabilistically or integrated with deterministic approach are recommended basis for reconciliation and summation.


The determination, classification and reporting of petroleum resources are of fundamental importance to the oil and gas industry. The use of consistent definitions and classification are essential as the numbers are important in development, operational and financing decisions. The near and long term petroleum planning activities depend on reliable assessment of the resources portfolio. Commercial discovery is a critical event and changes in reserves are key indicators of the success of nation's reserves replacement. The ability of a nation to replenish the reserves quantities through discovery or acquisition of additional reserves is crucial in sustaining petroleum long term viability. The downward revision of nation's resources greatly impact planning and policy decision, including the strategy to sustain nation's petroleum activities for as long as possible.

Complete inventory of resources classification provides a continuous process of estimation, classification, and depletion of the petroleum endowment. Furthermore, the numbers are also critical in relevant planning and policy decisions by government.

Lack of coherent definitions, classification and assessment of resources/reserves within companies operating in the country have presented difficulties with summation, reconciliation and overall management of the nation's resources/reserves portfolio. Thus, the effort to generate a consistent definitions and classification of resources/reserves was done to ensure a proper and effective management of nation's petroleum resources.

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