AbstractCompositing of sediment or water samples provides an opportunity to screen numerous samples economically if contamination is a relatively rare occurrence. However, standard compositing procedures simply identify that contamination exists among one or more constituent samples of the composite. Using a two‐way compositing strategy, detected contamination in composited samples can be attributed directly to constituent samples without further analyses. Procedure is illustrated using benthic sediment samples contaminated with crude oil following an oil spill. The proposed compositing scheme has a relative efficiency ofn/2 compared to the analysis of individual samples whenn2is the number of samples screened (e.g.,n2= 16 samples, relative efficiency is 4/2 = 2