A thesaurus, by definition, is "...a controlled vocabulary arranged in a known order in which equivalence, homographic, hierarchical, and associative relationships among terms are clearly displayed and identified by standardized relationship indicators, which must be employed reciprocally. Its purposes are to promote consistency in the indexing of documents, predominantly for postcoordinated information storage and retrieval systems, and to facilitate searching...." (National Information Standards Organization (NISO), Z39.19 - 1993).

Petroleum Abstracts uses a set of two thesauri and their supplemental lists.

The E&P Thesaurus is a collection of words and phrases that are descriptive of the concepts and equipment pertaining to petroleum exploration, development and production, exclusive of geographic areas and named geologic terms, which are included in the Geographic Thesaurus and its supplement. Further, the E&P Thesaurus is a controlled vocabulary for this subject area, in which the various concepts have been linked by means of generic or hierarchical relationships. These relationships may be truly generic or may be associations by use, or even convenience. Synonyms are handled as follows: all terms of like meaning are directed to one term for use as the index term for that particular concept. This selection usually follows popular usage and the patterns set by existing terms in the Thesaurus. The chosen term is called a "valid" index term; the other like terms are called "invalid" and are not used for indexing.

The E&P Thesaurus terms are interrelated on the concept-oriented (faceted) principle, and all descriptors are narrower terms of one of ten facet headings. These ten facets, which appear alphabetically, are as follows:

COMMON ATTRIBUTE
EARTH AND SPACE CONCEPTS
ECONOMIC FACTOR
EQUIPMENT
LIFE FORM
MATERIAL
OPERATING CONDITION
PHENOMENON
PROCESS
PROPERTY

The Geographic Thesaurus contains a listing of sedimentary basins, geographic features, and geographic area terms and their relationships. Its format is patterned after the E&P Thesaurus in a hierarchical fashion. The Geographic Thesaurus : Supplemental Terms contains the names of formations, groups, series, oil fields, anticlines, faults, counties, and similar terms that are not included in the Geographic Thesaurus proper. The E&P Thesaurus contains a set of terms for "Earth and Space Concepts" (e.g., DEPOSITIONAL ENVIRONMENT, FACIES, and BASIN) that are closely related to the terms in this Thesaurus.

All Geographic Thesaurus descriptors are part of a hierarchy which provides a compact listing of the terms in their structured form. WORLD is the top level of hierarchy for the Geographic Thesaurus. The terms at the next level down, which appear alphabetically, are as follows:

AFRICA
CENTRAL AMERICA
EURASIA
NORTH AMERICA
OCEANIA
SEAS AND OCEANS
SOUTH AMERICA

The Geographic Thesaurus vs. its Supplement:

Geographic Thesaurus:

Countries; States & provinces; Divisions of states (WEST TEXAS); Geographic areas (LA PAZ AREA); Geographic regions (ARAL REGION); Continents; Divisions of continents; Oceans & seas; National parks; Named geographic features:; Bays, gulfs & straits; Coasts & beaches; Ridges & mountains; Valleys, canyons & plains; Lakes & lagoons; Peninsulas & islands; Deserts; Sedimentary basins, troughs & embayments; Coal fields and basins; Submarine fans & canyons; Broad, basically structural, features: Uplifts, belts, arches, fault systems, fault belts, fracture zones, folded belts, & geosynclines, and other broad features; Platforms, shelves, pendants, scarps, & escarpments, and other similar terms

Supplement:

Formations, groups, & series; US counties & parishes; Oil & gas fields; Named geologic features: Anticlines & synclines, Faults & folds, Grabens & horsts, and other similar terms

[The Exploration and Production Thesaurus contains the technical vocabulary used for geologic structures, rock types, earth age, and depositional and tectonic concepts.]