This paper discussesthe outlook for Large Grid Block (LGB) models as predictive tools. The interactions between viscous fingering and heterogeneity are considered for combinations of secondary miscible, immiscible, and continuous and Water-Alternate-Gas injection tertiary miscible displacements. The approach uses detailed simulations in very fine-scale heterogeneous grids to calibrate simpler analytic and coarse grid models. It concludes that although much progress can be made in calibrating continuous solvent injection LGB models, these same models prove to be less reliable for more complicated situations, such as Water-Alternate-Gas injection. In particular, for continuous solvent injection: (1) The mixing parameter model can be calibrated with a potentially measurable indicator of heterogeneity to match secondary miscible recovery and injectivity. (2) Integrations between heterogeneity and effective relative permeability can be calibrated with this same indicator of heterogeneity. (3) These calibrations for secondary miscible and purely immiscible displacements can be combined and reasonably applied to tertiary miscible displacements. However, severe complications arise when considering Water-Alternate-Gas injection, particularly in heterogeneous systems which are not at their residual saturation. These complications result because: (1) The mixing parameter must vary with WAG ratio and cycle size. (2) The effective relative permeabilities depend on the nature of the phase being injected. In these situations, it is not possible to simultaneously match breakthrough times, recoveries and injectivies using a single set of LGB parameters.