As one of the most important electron acceptors in biology, oxygen is of particular interest as a factor in many microbial and biogeochemical processes. Gradients of molecular oxygen are of particular interest due to the fact that many important biological processes either occur at interfaces or are regulated by the flux of oxygen and other resources. The incorporation of chemical sensing within microfluidic structures, and the imaging of chemical concentrations therein, present particular challenges. Nevertheless, microfluidic structures offer unique opportunities to create microenvironments that set up gradients and environmental conditions that are relevant to biomedical or natural biogeochemical systems. In addition, chemical oxygen imaging creates the opportunity to identify hot spots or hot moments where biological activity is occurring. Here we describe primarily approaches to sense oxygen concentrations and gradients within microfluidic structures, using localized films of fluorescent oxygen sensing dyes. In addition, chemical imaging is described for macro-scale systems where chemical sampling timing and spatial location can be triggered by the observation of hot spots or hot moments. Diverse approaches will be contrasted for fabricating and imaging oxygen sensing devices and apparatus, including microfluidic pore network structures as models for natural systems at the pore scale.