This paper presents a definitive account of the effect of wettability on oil recovery from Berea sandstone based on the results of more than 50 slow-rate laboratory waterfloods. Closely reproducible wettability conditions and waterflood recoveries were obtained with wettability, depending on the crude oil, brine composition, aging temperature, and initial water saturation. Maximum oil recovery by waterflooding was obtained at very weakly water-wet conditions from shortly after breakthrough up to discontinuation of the test at 20 PV of water injected. In most of the tests, coproduction of oil and water continued long after breakthrough.