The morphological variation of complex drops of oil/water/oil (O/W/O) in unstable polymer/water/surfactant systems was investigated. A new, but simple, technique was developed to measure the internal phase ratio of multiple drops. The morphology change occurred because of inclusion of oil droplets into the dispersed water drops which contained water-soluble surfactant. The variation in morphology can lead to a delayed phase inversion if a substantial variation in the effective volume fraction of the dispersed phase occurs. The time sequence of the morphology change of complex drops is as follows: In the early stage of stirring, most water drops that are formed contain no internal oil droplets but some contain large internal oil droplets. As time proceeds, the relative size of the internal oil droplets to that of surrounding water drops is appreciably reduced, while the water drops become richer in the continuous phase. The progressive increase in the internal phase ratio of the dispersed phase will continuously increase the effective volume fraction of the dispersed phase and hence enlarge the water drop size. Eventually a balance might be reached between drop inclusion and escape, to give a steady-state, at which the drop morphology and size reach a constant value. If the rate of inclusion exceeds that of escape, so that a steady-state is not reached, a phase inversion will occur. The extent of variation in drop morphology with time was found to depend on the size of drops, which is highly influenced by the volume fraction of the dispersed phase, and the surfactant concentration in the system, which enables the water drops to entrain a larger volume of the continuous phase. The large drops are able to entrain a larger volume of the internal oil phase and, thus, contribute more to increasing the effective volume fraction of the dispersed phase and to inducing a phase inversion.