A high-pressure system designed to provide stable continuous combustion of a liquid-fuel spray under closely controlled reproducible conditions at pressures appropriate to those of the diesel-engine cycle is described. The system provides ready access and sufficient time for samples to be taken from the exhaust gases and from locations inside the flame. The results were compared with currently available mathematical models. Comparison with predictions from a relatively simple and efficient spray combustion model has been made using three soot formation models. Soot concentration rises to a peak and falls along the chamber with higher peak magnitude predicted at higher pressure and higher input equivalence ratio. Maximum concentrations are predicted in an annulus around the position of the peak axial value. Predicted values of equivalence ratio and soot concentration are shown to be in qualitative agreement with those obtained experimentally.