A review of ultimate recovery efficiency in 450 mature clastic fields from around the world provides a series of b enchmarks for evaluation of the redevelopment potential of old fields. Key determinants of ultimate recovery are fluid type/viscosity, matrix permeability and reservoir architecture. Development strategies and reservoir management techniques play crucial roles in maximizing expected ultimate recoveries for given reservoir/fluid parameters. Five main fluid type/permeability clastic-reservoir classes, with characteristic ultimate recovery distributions and controls, are: (1) heavy oil/tar reservoirs, in which RF is controlled by well spacing/reservoir depth, reservoir connectivity and the application of tertiary recovery techniques; (2) low-permeability oil reservoirs, in which RF is controlled by permeability variations, well spacing and application of waterflooding/miscible flooding, fraccing and horizontal drilling; (3) intermediate-permeability oil reservoirs, in which RF is controlled by fluid viscosity variations, reservoir heterogeneity/architecture and application of waterflooding; (4) high-permeability oil reservoirs, in which RF is controlled by natural drive strength/type and control of aquifer and gas-cap encroachment; and (5) gas/condensate reservoirs, in which RF is controlled by permeability variations, aquifer encroachment and condensate drop-out. Examination of actual case histories improves confidence in predevelopment predictions of recovery efficiency and shows what is possible in new or old fields.