Twenty-seven samples of feldspathic phyllarenite were obtained from three 1 m grids in a large, homogeneous distributary-bar sandstone body with the goal of elucidating bed-scale diagenetic heterogeneity. Significant variability in the content of both detrital and diagenetic components is present in the sample set. This variation is within the range of values predicted from comparison with a large regional data set from the same formation, but nonetheless, it is large enough to preclude successful prediction of diagenetic properties from consideration of average composition and thermal history alone. Grain size is one important local control on the overall abundances of cement and porosity. Grain size operates to control the overall degree of cementation (in these particular rocks, indirectly) through its influence on lithic grain content and, hence, on compaction. Relatively minor carbonate cement is an exception to this trend and appears to be distributed somewhat randomly, without regard to the size or composition of the detrital components. Diagenetic heterogeneity of the magnitude documented in this example is correlated to differences in porosity and permeability and therefore has implications for reservoir simulation and exploration risk assessment. Prediction of rock properties through diagenetic modeling is more successful if the textural controls on diagenetic heterogeneity are considered.