Laminar burning velocities of hydrocarbon blends of relevance to natural gas combustion, with addition of 0, 10, 35 and 50% hydrogen, were measured using the heat flux method. Hydrocarbon blends were methane (80%)/ethane (20%), methane (80%)/propane (20%) and methane (80%)/ethane (10%)/propane (10%), and in addition experiments were performed using pure methane as a fuel. For the first time it was shown experimentally that hydrogen promotes laminar burning velocity of blends with heavier hydrocarbons to a smaller extent than the well-studied effect on methane. Measurements show that enrichment by hydrogen results in 20-40% lower increase in laminar burning velocity for hydrocarbon blends compared to pure methane, depending on stoichiometry. Modeling points at the importance of increasing concentrations of OH, O and H radicals in H-2 enriched flames. At lean conditions increase in H atom concentration is of particular importance. The results are rationalized based on asymptotic flame theory analysis. (C) 2016 Elsevier Ltd. All rights reserved.