Ubiquitous oxygen (O(2)) is one of the most important analytes to be assessed in medicine, industry and the environment. Due to a number of advantages, miniaturized optical sol-gel sensors are rapidly replacing older electrochemical sensors. This account provides an overview of fluorinated organically modified silicate (ORMOSIL) xerogels as optical chemical sensors and shows how, together with the dye quenching rate, the subtle structural features of an organofluoro-silica matrix is of fundamental importance in determining the overall sensor performance.