The capabilities of the crossed molecular beam (CMB) method with mass spectrometric detection in the study of multi-channel elementary reactions of relevance in combustion chemistry are illustrated by several examples of reactions involving atomic oxygen and unsaturated hydrocarbons (acetylene, ethylene and allene), as well as hydrocarbon radicals (methyl and allyl). These systems have been investigated in our laboratory by resorting to soft electron impact ionization. Important information on the nature of the primary products and their branching ratio is reported and the implications for the modeling of combustion chemistry commented on. (C) 2011 Elsevier Ltd. All rights reserved.