Oil and gas reserves represent the most significant asset for any petroleum company. Without a common approach to classification, categorization and estimation petroleum in-place and recoverable volumes, it would be very difficult to know whether those estimates are: (a) comparable from one company to another, and (b) whether a discovered field can be developed commercially (reserves) or not (contingent resources). Reserves base and associated viable commercial development opportunities available are not only necessary but also critical for making rational investment decisions continually to sustain a reasonable annual growth rate for the company and ensure its long-term viability.

In an increasingly global economy and similar to international oil companies (IOCs) or the majors; more exploration and production companies (public and private) and state-owned national oil companies (NOCs), have been (a) acquiring petroleum assets outside their countries; (b) enter into partnerships (or joint ventures) with other companies, and (c) requiring external financing for their investment projects. This global trend has provided the main impetus and the opportunity for ever increasing international effort exhorted over the past decade to develop a set of common global technical standards that can be used to consistently and transparently define, estimate, classify, and categorize petroleum resources and reserves which are comparable worldwide. The unified guidelines are required to meet the needs of a wide range of global industry stakeholders, including the E&P companies (independents, IOCs and NOCs), financial institutions, regulatory agencies and governments.

The "Petroleum Resources Management System" (PRMS) [SPE-PRMS (2007)] provides such a desired global guidance that achieves a high level of consistency in the estimates of petroleum resources and reserves. The SPE-PRMS (designated as such for convenience) was developed by the SPE (Society of Petroleum Engineers) Oil and Gas Reserves Committee (OGRE) with valuable contributions from the following co-sponsoring organizations: the World Petroleum Council (WPC), the American Association of Petroleum Geologists (AAPG) and the Society of Petroleum Evaluation Engineers (SPEE).

Saudi Aramco has always been using the internationally recognized and accepted standards for estimating and booking its petroleum reserves. The company has voluntarily and deliberately adopted the use of SPE definitions and guidelines, including its published updates such as the SPE-PRMS (2007), in order to maintain desired consistency and transparency in and help ensure comparability.

The objective of this paper is to briefly describe, and further clarify key attributes of the SPE PRMS (2007) document with carefully selected additional technical and economic terms, statements and illustrations developed (and practiced) over many years while working with and addressing questions (e.g., seeking simplified, direct and explicit answers) raised and discussed among practitioners and managers of petroleum resources assessment and management systems.

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