Axisymmetric laminar jet diffusion flames in unconfined coflowing air are analyzed by using a boundary-layer description, the Burke-Schumann limit and the Shvab-Zel'dovich mixture fraction. The analysis focuses in hydrocarbon fuels, for which the stoichiometric mixture fraction takes very small values, leading to a significant simplification of the problem. Gravity effects are taken into account, identifying a parameter whose value provides a criterion to determine when buoyancy effects are dominant and, hence, to distinguish clearly between nonbuoyant and buoyant flames. A rational and physically sound choice of the characteristic values of the problem leads to dimensionless variables in which flame properties are weakly dependent on the parameters. Experimental measurements of stoichiometric heights of flames are compared with theoretical results, showing a good agreement.