Detailed flame measurements are necessary for the development of accurate chemical kinetics models. This study characterizes quasi one-dimensional, laminar, nearly adiabatic, and freely propagating flames stabilized over a Hencken flat flame burner. Major reactant and product species in lean premixed methane/oxygen/argon and ethylene/oxygen/argon flames were measured through extractive sampling and absorption spectroscopy to obtain spatially-resolved species profiles of oxygen, methane, ethylene, carbon monoxide and carbon dioxide. Experimental results were compared to numerical simulations of one-dimensional, freely propagating, adiabatic flames. Experimental and numerical results for flame speeds and species concentrations were largely in agreement within calculated uncertainty, indicating that data produced using a Hencken burner at sub-atmospheric pressure can be readily compared to numerical simulations without the need for flame or burner temperatures, which are prone to uncertainty. The influence of the extractive probe on flame structure was also investigated, and results suggest that the structure is less influenced by probe intrusion when the flame is highly stretched. (C) 2015 The Combustion Institute. Published by Elsevier Inc. All rights reserved.