A hydrocarbon reservoir has a distinctive shape, or configuration, that prevents the escape of hydrocarbons that migrate into it. Geologists classify reservoir shapes, or traps, into two types;
strudtural traps: a deformation in the rock layer that contains the hydrocarbons. Examples; fault traps and anticlinal traps.
stratigraphic traps:form when other beds seal a reservoir bed or when the permeability changes within the reservoir bed itself.
combination trap:this happens when more than one kind of trap forms.