Abstract: A mini-diluter apparatus and method are provided for preparing dilute samples of exhaust gas for emission testing. The apparatus includes first and second mass flow controllers which respectively control the mixing of exhaust gas and diluent gas samples at a constant ratio. The mixture is fed at a pressure, controlled by a back pressure regulator, to a third mass flow controller. This third controller provides a controlled sample rate (normally proportional to exhaust flow from an engine under test) to a bag sample system, or other sampling system, with excess mixture being exhausted through a pressure regulator to atmosphere. Improved accuracy and reduced calibration complexity are results of the improved apparatus and method.