A recently developed in situ FTIR method of monitoring CO2 evolution during oxidation of paint films has been used to measure CO2 produced by alkyd paints when enclosed in a high humidity oxygen atmosphere. Evolution of CO2 from paint films in the dark was observed and was found to persist over long periods. It is likely that this is the result of beta-scission of fatty-acid side-chains which accompanies oxidative cure of alkyd films: it decreases as these processes go to completion. The rate of CO2 evolution from aged films is reduced after the initial rate of cure has been accelerated by oven ageing or by increasing the concentration of catalytic driers. It has also been shown that resistance to photo-degradation increases as ageing of the films proceeds. Our results demonstrate that the sensitivity of CO2 detection by FTIR provides a useful method for following film cure and ageing. The technique has wider potential, e.g. for the study of oxidation in food oils and cosmetic preparations.