In this study, a comprehensive transient model was developed for multilateral wells producing from multiple formations separated by impervious streaks. The model is flexible and is capable of simulating the flow with any number of layers, unequal initial layer pressure, non-uniform petrophysical properties for each layer, and unequal layer size. Additionally, each lateral can have non-uniform formation damage and may be selectively completed. We investigated the long-term rate decline and cumulative recovery response of the multilateral wells connecting multiple isolated formations. Total flow rate, cumulative production, and fractional rate for each branch are all compared for several completion scenarios and layer properties. Crossflow between the layers through the wellbore is also evaluated.