The distribution of air mass flowrate between the cylinders of a 4-cylinder, carburetted automotive engine has been measured using a propane injection technique. The results show that over a wide range of operating conditions the engine has acceptably uniform distribution of air flow. At low- and medium-speed conditions the insertion of quite large obstructions into individual limbs is shown to have little effect on the air mass flows through these limbs. Only at high engine speeds and loads do these resistances have significant effect. The measured data are compared with corresponding predictions from a computer model of the engine and good agreement is shown.