This paper deals with the effect of the swirl number (0-0.8) on combustion characteristics of hydrogen-containing fuel blends in a gas-fired combustor. The present study is a numerical study that has been performed by using a commercial CFD (computational fluid dynamics) code. Selection of coherent combustion model is very important for more accurate prediction in the reactive modelling. Because of that, the PDF/Mixture Fraction combustion model has been selected due to better capturing the experimental results and is preferable for blending fuels. The other mathematical models used in this study are k-epsilon realizable turbulence model of turbulent flow and P-1 radiation model. Methane as baseline fuel has been modelled to verify the predictions. It is shown that predictions are in good agreement with the existing experimental data. Then, the hydrogen-containing fuel blends have been modelled to find out the effect of the swirl number on combustion characteristics of these fuels with five different swirl numbers from 0 to 0.8 at interval of 0.2. It is concluded that the flame temperatures are highly affected depending on changes of the swirl number. Because, tangential velocity of the air stream changes the temperature distribution in the combustor considerably. It is also demonstrated that changes in swirl number lead to position of the high NOx regions. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.