During the continuous catalytic hydrodeoxygenation (HDO) of cracked vegetable oil (CVO), CO 2 and CO occur as the main reaction gases, in addition to hydrocarbon gases such as CH 4 and C 2 H 6. The catalysts used were cobalt-molybdenum (CoMo) on an Al 2 O 3 support and platinum (Pt) on an active carbon. All named gas components can result directly from the decomposition of CVO. The results of batch experiments for gas phase reactions (GPRs) under the same 50 bar H 2 atmosphere using the same catalysts (CoMo, Pt) indicate that CO and CH 4 can also be formed by GPRs. CO can result from the reverse water-gas shift reaction (RWGS), and CH 4 from CO-or CO 2-methanation. The found CO-yields from GPRs are within the theoretical thermodynamic limits based on equilibrium. An unexpected inhomogeneity of the gas component concentrations in the reactor during batch investigations was observed despite the elevated temperature (380°C) and high RPM (1100) due to the high density difference compared to H 2, especially in the case of CO 2. Keywords Catalytic hydrodeoxygenation Á Cracked vegetable oil Á Biofuel Á Gas residence time Á Gas phase reactions Á Gas phase inhomogeneity

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