In time, much of the gas found its way into porous rocks, sometimes forming vast reservoirs, or gas fields, that were sealed beneath a layer of impermeable rock.
Aegade jooksul tungis suur osa sellest gaasist poorsetesse kivimitesse, nii et mõnikord moodustusid gaasikindla kivimikihi alla hiigelreservuaarid ehk gaasimaardlad.