Fractured petroleum reservoirs provide considerable challenge in studying natural depletion, immiscible gas injection, miscible, gas injection. and water injection. In this overview, certain key aspects of two-phase flow in relation to gas injection and water injection in fractured reservoirs are reviewed. One main conclusion from the review is that the field performance can be very efficient by water injection in some weakly water-wet fractured reservoirs despite the poor recovery in the laboratory by the conventional imbibition tests.