Trap identification is a first step in prospect evaluation and an important part of any exploration or assessment program. Future success in exploration will depend increasingly on an improved understanding of how traps are formed and an appreciation of the numerous varieties of trap types that exist. We define a trap as any geometric arrangement of rock that permits significant accumulation of hydrocarbons in the subsurface. A trap must include a reservoir rock in which to store hydrocarbons, and a seal or set of seals that impede or stop migration out of the reservoir. Although it is the geometric arrangement of reservoirs and seals that determines if a trap is present, both reservoir and seal analysis should be an integral part of trap evaluation.

Traps can be divided into three broad categories: structural traps, stratigraphic traps, and combination traps, which exhibit both structural and stratigraphic elements. We have subdivided structural traps into fold traps, traps associated with faults, traps associated with piercement features, and combination traps that require elements of both faults and folds for effectiveness. Stratigraphic traps can be grouped into primary or depositional traps, traps associated with unconformities (either above or beneath the unconformity), and secondary or diagenetic stratigraphic traps. We note that although each trap has unique characteristics, early recognition of trap type will aid in mapping and evaluating a prospect.