Differential Optical Absorption Spectroscopy (DOAS) has proven to be an extremely useful technique for retrieving trace gas columns from atmospheric measurements of reflected solar irradiance. We show that the use of DOAS is strongly constrained by the complexity of the absorption spectral structure that may be sampled by individual pixels in a detector array (for example, in the vibration-rotation bands of many species in the visible and infrared). To this end we introduce a Spectral Structure Parameterization (SSP) modification to DOAS which depends primarily on structure in the absorption cross-section of the atmospheric species intended for retrieval. We show that DOAS-SSP may be used to determine which absorption spectra are suitable, in terms of complexity of absorption structure, for use in DOAS retrievals as well as how to extend DOAS trace gas retrieval to those species with highly-structured absorption spectra. ¿ 2000 American Geophysical Union