A best-fitting procedure for the quantitative determination of the molar fractions of the stereosequences that define the microstructure of an ethylene−norbornene (E−N) copolymer from ¹³C NMR spectra has been set up. The quantitative determination of copolymer microstructure will allow one to clarify the E−N copolymerization mechanism. This method utilizes the observed peak areas of the ¹³C signals and takes into account the consistency between peak areas and the stoichiometry of the copolymer chain. Thus, a further extension of signal assignments is made possible by guessing assignments of unknown signals and by discarding inconsistent hypotheses. This procedure has been applied to the analysis of the ¹³C NMR spectra of a large number of E−N copolymers, prepared with catalyst precursors rac-Et(indenyl)₂ZrCl₂ (1), rac-Me₂Si(2-Me-benz[e]indenyl)₂ZrCl₂ (2), Me₂Si(Me₄Cp)(N^tBu)TiCl₂ (3), and Me₂C(Flu)(Cp)ZrCl₂ (4). An estimate of the molar fractions of the various stereosequences with a standard deviation on the order of 1−2% has been obtained. The comparison between controversial assignments existing in the literature for a number of ethylene signals has confirmed our previous assignments. New signals such as those of the C2/C3 carbons of EENNEE meso sequences (M) and of the external carbons C5 of MM and MR triads in ENNNE sequences have been assigned.