Although attention is given to the composition of the injected brine in a waterflood with respect to compatibility with the formation, tests are not usually made to determine its effect on oil recovery. This study shows that the wettability and laboratory waterflood recoveries of crude oil/brine/rock (COBR) ensembles can be strongly dependent on brine composition and on related COBR interactions. The sensitivity of these interactions to temperature and crude oil composition is also demonstrated.