Effects of fuel variability involving small fluctuations in fuel composition on physicochemical properties of premixed biogas-hydrogen combustion are quantified using global sensitivity analysis approach. Different proportions of hydrogen addition, and different CH4:CO2 ratios in biogas-hydrogen fuel with uncertainties are investigated from a statistical point of view. Analyses show that small fluctuation of biogas-hydrogen fuel composition does not lead to significant fluctuations in physicochemical properties of combustion such as laminar flame speed and adiabatic flame temperature. A fast growth of laminar flame speed fluctuation from lean to rich combustion of biogas-hydrogen fuel is observed implying a less stable flame at rich condition, and lower dimensional studies show that hydrogen uncertainty takes predominant responsibility for the rapid increase of flame speed. Apart from the uncertainty of hydrogen, it is found that carbon dioxide concentration fluctuation has a larger negative effect on stabilising biogas-hydrogen flame compared to that of methane. It is also found that for biogas-hydrogen fuel with high hydrogen content, contribution of carbon dioxide variability to flame speed fluctuation decreases while methane contribution increases. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.