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The stratigraphic distribution of BCGAs extends from the Cambrian through the Eocene (Table 1). However, there appear to be some differences in the stratigraphic distribution of direct and indirect BCGAs. For example, the preponderance of direct BCGAs occur in Cretaceous through Eocene rocks (Table 1), whereas indirect BCGAs more commonly occur in pre-Cretaceous rocks. Although some of the apparent difference in stratigraphic distribution may be attributable to the disproportionate number of studies in Cretaceous and younger rocks compared to numbers of studies in pre-Cretaceous rocks, the question of seal integrity in direct systems arises. As previously discussed, the effective life of capillary pressure seals in direct systems is not known; therefore, because of the perceptions of a leaky seal in direct systems, the occurrence of direct systems in pre-Cretaceous rocks may be less common than in Cretaceous and younger rocks. Some examples, however, of pre-Cretaceous direct BCGAs include Permian rocks in the Timan-Pechora basin, Russia (Law et al., 1996), and the Sichuan basin, China (Da-jun and Yun-ho, 1994); Pennsylvanian rocks in the Arkoma basin (Meckel et al., 1992); and Carboniferous rocks in the Dnieper-Donets basin, Ukraine (Law et al., 1998b) (Table 1).

The stratigraphic distribution of BCGAs extends from the Cambrian through the Eocene (Table 1). However, there appear to be some differences in the stratigraphic distribution of direct and indirect BCGAs. For example, the preponderance of direct BCGAs occur in Cretaceous through Eocene rocks (Table 1), whereas indirect BCGAs more commonly occur in pre-Cretaceous rocks. Although some of the apparent difference in stratigraphic distribution may be attributable to the disproportionate number of studies in Cretaceous and younger rocks compared to numbers of studies in pre-Cretaceous rocks, the question of seal integrity in direct systems arises. As previously discussed, the effective life of capillary pressure seals in direct systems is not known; therefore, because of the perceptions of a leaky seal in direct systems, the occurrence of direct systems in pre-Cretaceous rocks may be less common than in Cretaceous and younger rocks. Some examples, however, of pre-Cretaceous direct BCGAs include Permian rocks in the Timan-Pechora basin, Russia<Lawetal_1996 /> and the Sichuan basin, China;<Da-junandYun-ho_1994 /> Pennsylvanian rocks in the Arkoma basin;<Meckeletal_1992 /> and Carboniferous rocks in the Dnieper-Donets basin, Ukraine<Lawetal_1998b /> (Table 1).

Indirect BCGAs occur in rocks ranging from Cambrian through Cretaceous. Examples include Cambrian and Ordovician reservoirs in the Ahnet basin of Algeria, Ordovician reservoirs in Jordan (Ahlbrandt et al., 1997), Lower Silurian reservoirs in the Appalachian basin (Davis, 1984; Law and Dickinson, 1985; Zagorski, 1988, 1991; Law and Spencer, 1993; Law et al., 1998a; Ryder and Zagorski, forthcoming), and Jurassic sandstone reservoirs in the Bossier Shale (Montgomery and Karlewicz, 2001; Emme and Stancil, 2002) in the United States Gulf Coast (Table 1).

Indirect BCGAs occur in rocks ranging from Cambrian through Cretaceous. Examples include Cambrian and Ordovician reservoirs in the Ahnet basin of Algeria, Ordovician reservoirs in Jordan,<Ahlbrandtetal_1997 /> Lower Silurian reservoirs in the Appalachian basin,<Davis_1984 /><LawandDickinson_1985 /><Zagorski_1988 /><Zagorski_1991 /><LawandSpencer_1993 /><Lawetal_1998a /><Ryder and Zagorski_forthcoming /> and Jurassic sandstone reservoirs in the Bossier Shale<MontgomeryandKarlewicz_2001 /><EmmeandStancil_2002 /> in the United States Gulf Coast (Table 1).

==References==

==References==