Carrier beds are lateral migration pathways that link source rocks with reservoirs in conventional petroleum plays. Carrier beds may—but need not—have the same reservoir properties as the conventional reservoirs supplied by them. Indeed, the downdip limits of many conventional fields are defined by changes in porosity and, more often, permeability, associated with a change in facies between the carrier beds and the reservoir. The low permeability of the carrier beds does not preclude them from supplying the reservoir at geological time scales. If sufficient porosity exists for economic volumes of hydrocarbons to be present, the low permeabilities that previously marked the economic limits of some fields need no longer preclude extension of the field downdip into strata that served as carrier beds for the conventional reservoir. Horizontal wells and multistage hydraulic fracturing allow low-permeability carrier beds to become viable hydrocarbon reservoirs. The east Pembina halo play in the Cardium Formation (Cretaceous) of western Canada and the offshore Mancos Shale play in the San Juan Basin, New Mexico, both produce from carrier beds that served as migration pathways for oil in conventional reservoirs. These plays are now interpreted as carrier bed plays, along with the Codell Sandstone (Cretaceous) of the Denver Basin and the Turner Sandy Members of the Carlile Shale (Cretaceous) of the Powder River Basin. Placing plays within a petroleum system framework by identifying them as carrier beds should help focus the search for similar plays in the future and extend the areal extent and life of analogous oil and gas fields.