The termination kinetics of the free-radical bulk copolymerization of dodecyl acrylate (DA) and methyl acrylate (MA) has been investigated at various monomer mole fractions between 15 and 50 °C and up to 2000 bar. The ratio of termination to propagation rate coefficients, (kt/kp)copo, is measured via the single pulse-pulsed laser polymerization (SP-PLP) technique. Chain-length averaged kt,copo are deduced from (kt/kp)copo in conjunction with kp,copo data that are estimated via a simplified version of the implicit penultimate unit effect (IPUE) model. At low and moderate degrees of monomer conversion extended ranges of almost constant kt are observed where termination is controlled by segmental diffusion with important contributions of steric effects. These plateau kt values are significantly - by almost two orders of magnitude - different for MA and DA. The increase with MA content of kt,copo is adequately described by a penultimate unit model which uses the geometric mean approximation for estimating rate coefficients of cross-termination between radicals of different free-radical terminus. The model applies within the entire pressure and temperature range of the present study. At high degrees of monomer conversion, at and above 50%, homo-kt and kt,copo are almost insensitive toward the composition of the monomer mixture. The termination rate under these conditions is essentially controlled by reaction diffusion.