The heat flux method for determining the adiabatic burning velocity of gaseous mixtures of fuel and oxidizer and also producing well-defined reference flames is described in detail. Practical aspects of the heat flux method are discussed, especially the construction of the burner and attachment of thermocouples. An analysis is given of possible uncertainties and ways of correcting shortcomings. Conclusions from this analysis are applied to a typical measurement. The results are compared to other published results, including those from other often used methods, such as those with counter flow and closed vessels. For methane and air, a peak value of S-L = 37.2 +/-0.5 cm/s was found. (C) 2003 The Combustion Institute. All rights reserved.