The present work analyses the effect on the reforming process of biodiesel crude glycerol of three impurities commonly found in this product. The influence of the presence of CH3OH (0-5 wt.%) and/or CH3COOH (0-3 wt.%) and/or KOH (0-2.8 wt.%) during the catalytic steam reforming of a 30 wt.% glycerol aqueous solution has been evaluated theoretically, studying the equilibrium composition of the gas, and experimentally in a fluidised bed reactor at 550 degrees C. The presence of the aforementioned impurities has a weak impact on the thermodynamic gas composition. However, they significantly influence the product distribution (in carbon basis) obtained experimentally. The carbon of the feed converted into gas, solid and liquid products varied as follows: 75-100%, 0-25% and 0-2.5%. CH3OH alone does not alter the results obtained with pure glycerol. In contrast, CH3COOH and KOH decrease the initial production of gases. This decrease is very high for KOH due to the formation of char. However, its progressive accumulation inside the reactor exerts a positive catalytic effect on the gasification of this char, augmenting the gas production overtime. The composition of the gas was little affected by the presence of the impurities. The gas phase was made up of a mixture of H-2 (66-70 vol.%), CO2 (24-29 vol.%), CO (3-6 vol.%) and CH4 (0.5-2.5 vol.%). The liquid phase consisted of a mixture of alcohols, ketones, cyclic compounds, aldehydes and phenols. (C) 2015 Elsevier B.V. All rights reserved.