A new method of Continuous Fractionation using a SPLITT cell is conceived, developed, and tested, and is demonstrated to be useful for separation of collections of particles with different sizes and densities. With this previously uninvestigated mode of operation, this is accomplished for particles by buoyancy-driven separation. Some of the capabilities of this system are illustrated by successful separations of different-sized fluorescent polymer microspheres, with different carrier densities. The resulting experimentally-measured fraction recovery variations are then in good agreement with theoretical calculation from buoyancy-driven SPLITT theory.