Electron paramagnetic resonance spectroscopy (EPR) allows the detection and quantification of radicals generated during autoxidation of lipids. Even though the high reactivities and very low steady-state concentrations limit the direct detection of lipid-derived radicals to near rigid systems at low temperatures, then the spin trapping technique makes it possible to study radical formation in most types of lipid-containing foods. The addition of radicals to spin traps generates EPR detectable spin adducts that can allow assessment of shelf life and evaluation of possible antioxidants. By analysis of EPR spectra of spin probes, which are stable radicals, the availability of dioxygen at a microscopic scale can be evaluated as well as the location of important components such as antioxidants in emulsion systems.