This paper presents nomograms that assist in the correct identification of the middle time region (MTR) straight line on a semilog or Homer plot of buildup data from a heterogeneous reservoir. These nomograms also provide a realistic assessment of the types of heterogeneity that affect the buildup data. The nomograms are a quantitative extension of the widely used derivative-analysis method. The heterogeneities considered cover lateral discontinuities in reservoir transmissibility, naturally fractured, and vertically stratified and lenticular formations.