Improved/enhanced oil recovery (IOR/EOR) has the potential to unlock a significant amount of residual and trapped oil from existing and new hydrocarbon resources. This chapter addresses the various IOR/EOR strategies in carbonates and sandstone reservoirs, including chemical EOR, and hybrid EOR procedures. Each of these EOR approaches has its own set of challenges and preferences when it comes to the environment where it is used. Recent investigations have provided new insights into COBR systems, which have helped to improve the performance of these EOR methods. Detailed awareness of COBR systems can aid in better implement EOR methods in the field to maximize oil recovery (i.e., cost-effective) while also reducing environmental impact (i.e., CO2 footprint). Consequently, the primary goal of this chapter is to increase the reader's understanding of the extent of fluid-fluid and fluid-rock interactions to enable efficient IOR/EOR project designs that accurately reflect the requirements of candidate reservoirs for upstream oil and gas applications. © 2023 Elsevier B.V.