Thirty-three [17.0-58.7 cm diameter] white, southern red, and scarlet oaks of dominant or suppressed crown position on two sites were inoculated at 1.4 m above ground level with mycelia of either of two isolates of Phytophthora cinnamomi in late July, 1994. Six months later the inoculated areas were debarked and observed for canker development. Cankers formed around mycelial plugs in 100% of the trees. Mean canker length/width for all species was 43.6/4.3 cm. From these observations, it appears that these species are very susceptible to this soil-borne pathogen. However, naturally occurring cankers on oaks have not yet been reported in the United States even though P. cinnamomi is common in southern Appalachian soils where these oak species are abundant.