Understanding the combustion chemistry of the butene isomers is a prerequisite for a comprehensive description of the chemistry of C1 to C4 hydrocarbon and oxygenated fuels such as butanol. For the development and validation of combustion models, it is thus crucial to improve the knowledge about the C4 combustion chemistry in detail. Premixed low-pressure (40 mbar) flat argon-diluted (25%) flames of the three butene isomers (1-butene, trans-2-butene and i-butene) were studied under fuel-rich (phi = 1.7) conditions using a newly developed analytical combination of high-resolution in situ molecular-beam mass spectrometry (MBMS) and in situ gas chromatography (GC). The time-of-flight MBMS with its high mass resolution enables the detection of both stable and reactive species, while the gas chromatograph permits the separation of isomers from the same sampling volume. The isomer-specific species information and the quantitative mole fraction profiles of more than 30 stable and radical species measured for each fuel were used to extend and validate the C4 subset of a comprehensive flame simulation model. The experimental data shows different destruction pathways for the butene isomers, as expected, and the model is well capable to predict the different combustion behavior of the isomeric flames. The detailed analysis of the reaction pathways in the flame and the respective model predictions are discussed. (C) 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved.