During this period, reservoir simulation matured into a three-phase, history-aware discipline that embraced fractured reservoirs, detailed relative permeability behavior, and automated matching workflows. Researchers focused on building three-dimensional, multi-well models that captured gravity effects, imbibition, and heterogeneity, while developing methods to estimate three-phase properties from limited data. The drive toward history matching and hysteresis-aware saturation functions established a pragmatic framework for predictive reservoir engineering.