Stagnant connate waters associated with oil fields are similar in ratios of ions and cations. The principal ion is chloride--nearly always 99 percent. The principal cations are sodium, calcium and magnesium, and the usual Ca/Mg ratio is 5 to 1 (in equivalent weights). The concentration ranges from about 50,000 to 350,000 ppm. There is a general tendency for this type of water to increase in concentration with depth. In artesian situations the compositions of oil field waters is different. They range in concentration from 5,000 to 15,000 ppm. Sodium is the predominant cation, 85 to 100 percent and calcium and magnesium are rare or absent. These waters are classified into two types by their anions: (1) those without SO 4 and HCO 3 from 3 to 85 percent and (2) those with more than 50 percent SO 4 .