During this period, chemical enhanced oil recovery matured as a discipline by merging chemical formulation with a rigorous understanding of displacement physics. Research emphasized multi-component surfactant systems to lower interfacial tension, manipulate rock wettability, and exploit microemulsion behavior, while extending fractional-flow concepts to more complex flows. The field increasingly recognizes capillary forces and wettability heterogeneity as central determinants of microscopic displacement, guiding both laboratory studies and early field strategies.