We report on an efficient method to concentrate suspensions in a flow channel comprising sparse periodic arrays of obstacles. The obstacle spacings are a few times larger than the diameter of the particles. We perform up-scaled experiments, in which all particles flow along a few obstacle lines rotated with respect to the main flow direction. We found that for a diluted suspension a single line is sufficient to displace all particles into a concentrated stream. With visual high speed camera images particle–particle interactions were observed at increasing concentrations. Although one obstacle line was no longer enough to retain all particles, few additional obstacle lines facilitated good separation. This provides the insight that while the angle of the lines determines the primary separation, the number of lines is coupled to the maximum particle volume fraction that can be separated. With CFD simulations we showed that the flow resistance in these sparse arrays is very low and that the flow distribution across the outlets is easily controlled by the outlet tubing. These conclusions show the potential of sparse obstacle arrays for effective concentration of suspensions.