Abundant ground-water resources underlie the Pascagoula River basin. These resources have been developed intensively in only a few places--namely, Hattiesburg, Laurel, Meridian, and Pascagoula. Seepage from the ground water reservoirs sustains the base flows of the Leaf, Chickasawhay, Pascagoula, and Escatawpa Rivers and their tributaries. The fresh-water-bearing section is 300 to 3,500 feet thick and is composed chiefly of sand and clay of Eocene to Recent age. Major rock units represented are the Wilcox, Claiborne, Jackson, and Vicksburg Groups and formations of Miocene and Pliocene ages. Aquifers in the Claiborne Group provide water for all purposes in the northern third of the basin. The Claiborne is underlain by the potentially important but virtually untapped Wilcox Group. Miocene aquifers are the main source of water supplies in the southern half of the basin, but Pliocene aquifers furnish most supplies in the Jackson County area at the basin's southern extremity. Much of the fresh-water section has undergone no water-supply development because of the great depth of many aquifers and the availability, at shallow depths, of supplies adequate for present needs. However, a large part of any substantial increase in ground-water withdrawal will probably come from wells deeper than those commonly drilled in the region. Ground-water levels are within 50 feet of the surface in most places, and flowing wells are common in the valleys and near the coast. Water-level declines due to pumping have become serious problems only in a few localities of heavy withdrawal. In most of these places redistribution of pumpage would alleviate the problem of excessive drawdown. Although few wells in the basin yield more than 500 gallons per minute, yields of 2,000 gallons per minute or more could be reasonably expected from efficiently constructed wells almost anywhere in the region. Total ground-water pumpage is estimated to be about 60 million gallons per day. Potential pumpage is many times that figure. Well fields capable of yielding several million gallons of water per day would be feasible in most places. The ground water is of good to excellent quality. Most of it is a sodium bicarbonate type of water. It usually is soft and has a low to moderate dissolved-solids content. Excessive iron is a problem in places, particularly where water supplies are obtained from shallow aquifers, but at least a part of the excess iron comes from corrosion of well and distribution-line fittings by slightly acidic water. Salt-water encroachment is a potential problem in the coastal area, but little increase in salinity has been observed in monitor wells in the period 1960-65. Saline-water resources are available for development at considerable depth in most of the region.