Water-rock interactions are responsible for the chemical aspects of mineral diagenesis. The main processes involved are dissolution of detrital and authigenic minerals, precipitation of authigenic minerals and mineral transformations including replacement, recrystallization and hydration/dehydration. The possible water-mineral interactions involved are determined by the chemical composition of pore water, the mineral composition of the reservoir rocks and the subsurface temperature and pressure. Understanding these processes is extremely important in the petroleum industry because they lead to major increases or decreases in the porosity and permeability of reservoir rocks. In the last 10 years organic species dissolved in subsurface waters and their inorganic interactions have become one of the most intensively studied fields in geochemistry. This increased interest stems from the realization that organic species, which may be present at very high concentrations (up to 10,000 mg/L) in subsurface waters (Carothers and Kharaka, 1978; Surdam and Crossey, 1984) can play an important role in mineral diagenesis (Kharaka and Mariner, 1977; Curtis, 1978; Schmidt and McDonald, 1979; Lundegard et al., 1984; Kharaka et al., 1985a). Dissolved organic species can play an important role in mineral diagenesis because of the following chemical properties. (1) They can be the dominant source or sink for the hydrogen ion (H), and thus, directly or indirectly control the pH and buffer capacity of subsurface waters. The pH of subsurface water is probably the most important chemical component that affects mineral diagenensis (Kharaka et al., 1980). (2) They form soluble complexes with metals and other inorganic species, thus enhancing