Simulation of hydrogen-air mixture explosions in a closed large-scale vessel with uniform and non- uniform mixture compositions was performed by the group of partners within the EC funded project "Hydrogen Safety as an Energy Carrier" (HySafe). Several experiments were conducted previously by Whitehouse et al. in a 10.7 m3 vertically oriented (5.7-m high) cylindrical facility with different hydrogen-air mixture compositions. Two particular experiments were selected for simulation and comparison as a Standard Benchmark Exercise (SBEP) problem: combustion of uniform 12.8%2(vol.) hydrogen-air mixture and combustion of non-uniform hydrogen-air mixture with average 12.6%2(vol.) hydrogen concentration across the vessel (vertical stratification, 27%2vol. hydrogen at the top of the vessel, 2.5%2vol. hydrogen at the bottom of the vessel); both mixtures were ignited at the top of the vessel. The paper presents modelling approaches used by the partners, comparison of simulation results against the experiment data and conclusions regarding the non-uniform mixture combustion modelling in real-life applications.