The name of a petroleum system labels the hydrocarbon-fluid system or distribution network (Fig. 2D) in the same way the name Colorado River designates an aqueous distribution system, the river and its tributaries. The name of the petroleum system includes the geological formation names of the source rock followed by the major reservoir rock (Fig. 2C) and then the symbol expressing the level of certainty. For example, the Deer-Boar(.) is the name of a hydrocarbon fluid system whose source rock, the Deer Shale, most likely generated the petroleum that charged one or more reservoir rocks, which in this case is the Boar Sandstone. It is the major reservoir rock because it contains the highest percentage by volume of hydrocarbons in the petroleum system.
A petroleum system can be identified at three levels of certainty: known, hypothetical, and speculative. At the end of the system’s name, the level of certainty is indicated by (!) for known, (.) for hypothetical, and (?) for speculative. The symbol indicates the level of certainty that a particular pod of active source rock has generated the hydrocarbons on the table of accumulations (Fig. 2C). In a known petroleum system, a well-defined geochemical correlation exists between the source rock and the oil accumulations. In a hypothetical petroleum system, geochemical information identifies a source rock, but no geochemical match exists between the source rock and the petroleum accumulation. In a speculative petroleum system, the link between a source rock and petroleum accumulations is postulated entirely on the basis of geological or geophysical evidence.
In certain frontier areas of the world, especially in the offshore, the stratigraphic units are poorly understood and frequently undesignated. Here, the judgment of the investigator is required. The geologist should avoid using ages, such as Jurassic, in the name because it fails to uniquely identify the petroleum system. Other situations arise where it is difficult or confusing to follow the naming rules. For example, when a rock unit that includes both the source and reservoir forms more than one petroleum system, the same name might be used more than once, such as Monterey(!) petroleum systems. Here, a geographic modifier can be used to differentiate the systems. Another naming problem arises in frontier areas where formal rock units are lacking, so only ages or geophysically mapable units are used. A geographic name or the name of an accumulation in the petroleum system may be used. If it is impossible to follow the formal designation of a petroleum system, the investigator should select a unique name that identifies the fluid system, not the rock units.