For several decades, the terminology used in the classification of petroleum reserves and resources has been the subject of study and ongoing revision. Since the mid-1930s, numerous technical organizations, regulatory bodies, and financial institutions have introduced ever more complex terminologies for the classification of petroleum reserves.
In addition, the evolution of technology has yielded more precise engineering methods for reserve evaluation and has intensified the need for an improved nomenclature to achieve consistency among professionals working with petroleum reserves terminology.
In recognition, the Society of Petroleum Engineers (SPE) and the World Petroleum Council (WPC, formerly World Petroleum Congresses) developed a set of petroleum reserves definitions which were presented to the industry in March 1997. These represented a major step forward in their mutual desire to improve the level of consistency in reserves estimation and reporting on a worldwide basis.
As a further development, SPE and WPC recognized the potential benefits to be obtained by supplementing those definitions to cover the entire resource base, including those quantities of petroleum contained in accumulations that are currently sub-commercial or that have yet to be discovered.
These other resources represent potential future additions to reserves and are therefore important to both countries and companies for planning and portfolio management purposes. In February 2000, the two organizations in conjunction with the American Association of Petroleum Geologists (AAPG), developed resources definitions that encompassed the entire range of petroleum reserves and resources.