The kinetics and mechanisms involved in the ring-opening metathesis polymerization of 5-norbornene-2-yl acetate (NAc) and cyclooctadiene (COD) in dichloromethane (DCM) were quantified using automatic continuous online monitoring of polymerization (ACOMP). The results yielded time-dependent monomer conversion and the effects of temperature and reactant concentration, evolution of weight-average molecular mass M-w, and intrinsic viscosity [eta](w). The evolution of the molecular mass was generally consistent with a "living" mechanism in a rapid first phase, where expected target masses for p(NAc) were met, but often revealed a secondary, slight degradative phase. In contrast, p(COD) yielded molar masses far below target values and generally showed a more pronounced degradative phase. These latter two phenomena for p(COD) appear to be symptomatic of a mechanism that shortens chains with concomitant increase in polydispersity. Furthermore, through a combination of M-w, viscosity, and concentration dependencies it was deduced that the slow degradative phase for both p(NAc) and p(COD) is due almost entirely to cross-metathesis reactions. A probabilistic analysis for cross-metathesis supports these assertions. Automatic continuous mixing (ACM) was used to measure second virial coefficients and intrinsic viscosity, and these are consistent with polymers having large solvent domains and strong interactions for p(NAc). In a further application, a second addition of monomer during reactions revealed that no observable termination takes place over time. Results were cross-checked by conventional multidetector gel permeation chromatography (GPC). Ultimately, this method should help in the control of reactions to produce highly specific polymers and architectures.