The adequate consideration of resource interactions among IS projects is a challenging but important requirement within IS project portfolio selection. However, the literature is silent on potential techniques for the identification and assessment of resource interactions. Moreover, the literature has so far neglected the question of the trade-off between time and effort invested in identifying and evaluating resource interactions caused by resource sharing among projects, compared to the benefits derived from this exercise, and the extent to which it is worth doing so thoroughly. Hence, our contribution is twofold. First, we suggest a technique to support the identification and evaluation of potentially economically relevant resource interactions. Second, we propose a decision model that allows to calculate a theoretical upper bound for the amount of effort that should be invested in improving estimates for identified interactions as part of the portfolio planning process.