Carboxylic acids are valuable chemical products, which can be produced efficiently by catalytic oxidation of various organic compounds using vanadium-based catalysts. Degradation resistance of carboxylic acids under applied reaction conditions is an important factor influencing selectivity of such reactions. This paper addresses the oxidative and non-oxidative gas phase degradation of formic, acetic and propionic acids over V2O5/TiO2 and MoVTeNb mixed oxides. Formic acid has been found to undergo mainly acid catalyzed decarbonylation, regardless the presence or absence of oxygen in the feed. Both acetic and propionic acids underwent oxidation (in aerobic conditions) through one-carbon degradation steps until CO and CO2 were produced. The mechanistic aspects of these transformations are discussed. The key intermediacy of 2-(hydro)peroxy carboxylic acids is suggested, based on the nature of primary reaction products. The catalytic activity of MoVTeNb mixed oxides toward oxidative and non-oxidative degradation of acetic and propionic acids appeared notably lower compared to that of V2O5/TiO2. This may be linked to the enhanced efficiency of the former catalyst in selective oxidation of organic substrates to carboxylic acids. (C) 2013 Elsevier B.V. All rights reserved.