**1. Introduction**

Waterflooding is the most widely used method to increase oil recovery. Recent studies show that in many cases, by modifying the salinity and ionic content of the injected water, oil recovery by waterflooding improves. The injection of water with lower salinity or adjusted ion composition triggers different mechanisms that modify the wettability of sandstone and carbonate formations. The bonding of polar components in the crude oil with the carbonate or sandstone rock surface is affected by the salinity and composition of the injected water, which generally produces wettability alteration of the rock surface. Several mechanisms have been proposed in the literature for low-salinity water flooding EOR, such as fine migration, rock dissolution, pH increase, multicomponent ion exchange, and doublelayer expansion. The combination of these mechanisms is believed to affect the oil recovery in carbonate and sandstone formations. For more information on LSW and the governing mechanisms, the reader is referred to [1].

The idea of combining two (or more) EOR methods, known as hybrid methods, has been investigated recently to promote the activation of several oil recovery mechanisms to increase the ultimate oil recovery, tackle operational challenges, reduce environmental damage, and lower the production costs. Hybrid methods can be optimized for different injection scenarios to achieve the highest feasible recoveries. LSW flooding has been found to be effective when combined with gas injection (mainly CO2), surfactant and/or polymer flooding, nanofluid injection, and hot water injection, each of which can improve the oil recovery through several mechanisms such as mobility control, wettability alteration, IFT reduction, etc. Experimental and modeling studies reviewed in this chapter have found that LSW hybrid methods can provide up to 30% original oil-in-place (OOIP) incremental oil recovery.
