Tracers are used in well to well tests to gather data about the movement and saturation of fluids and hydrocarbons in the subsurface. Chemical tracers can be used to gather data about water or gas. This article discusses some of the commonly used chemical water tracers for well to well tests. Chemical tracers can also be used in a single well configuration to estimate residual oil saturation or connate water saturation. Application of several nonradioactive chemical tracers has been reported in the literature.