Abstract: The process is used to monitor the stability of compositions and reaction mixtures which contain vinylog compounds, more especially (meth)acrylic acid and/or (meth)acrylates. The content of dissolved oxygen in the composition or in the reaction mixture is determined and compared with predetermined reference values. Incipient or threatening polymerization is detected as early as possible and well before polymerization actually begins. Monitoring can be carried out simply, inexpensively and, in particular, safely both during storage and transportation and during the course of reactions, more particularly during the esterification of (meth)acrylic acid with mono- or polyhydric alcohols.