The unique chemical and physical properties of oil sands tailings require the development of new classes of polymer flocculants to achieve efficient flocculation and dewatering. Fast and direct performance measurements of flocculation and dewatering efficiency are essential for the development of new polymer flocculants. The microscopic characterization of settling velocity and size for free settling aggregates then allows the derivation of the aggregate density as a function of size. Aggregate density is an indication of the internal aggregate structure that directly influences sedimentation, resistance to shear, and dewatering. Aggregate structures formed during oil sands tailings flocculation with a commercially-available anionic polyacrylamide (A-PAM) were compared with that of novel hyperbranched functionalized polyethylene (HBfPE) flocculants, showing that aggregates made with some HBfPE formulations were denser and settled faster than those formed with A-PAM. This paper demonstrates that this approach can usefully quantify the structure of aggregates formed during the treatment of oil sands tailings with polymer flocculants.