This paper presented an experimental study about R134a and PAG oil upward flow in a vertical header of a microchannel heat exchanger. The flow configuration in the heat pump mode of reversible systems was mimicked in the experimental facility: the refrigerant-oil mixture was fed from the bottom pass and exits through the top pass. The inlet quality in the experiments was varied from 0.2 to 0.8, and mass flow rate is 4.19 g s-1 (0.0092 lb s-1). It has been seen that small amount of oil (OCR=0.5%) worsened the distribution. But further increasing the OCR to 2.5% and 4.7%, the distribution became better. The experimental quality distribution results were incorporated in a microchannel heat exchanger model to evaluate the evaporator performance. Initial numerical results showed that although the distribution was improved with more oil, the cooling capacity kept reducing. The capacity degradation compared with the uniform distribution case decreased due to theimprovement of distribution.