Pressure measurements and records of drill-stem tests (DST) from deep petroleum exploration wells in the Anambra basin have been analysed together with fluid potential data obtained from over 500 water wells drilled in the basin. The analyses indicate the existence of three distinct hydraulic systems in the basin, viz.: an upper system with hydrostatic formation pressures; a middle system in which pressures are just moderately higher than hydrostatic; and a relatively deep system of abnormally high formation pressures. The three hydraulic systems correspond approximately to three hydrostratigraphic units that are clearly discernible from the lithologie logs of boreholes and oil wells drilled in the basin. The main fluid in the uppermost hydraulic system is circulating meteoric water, and the fluid potential distribution is largely governed by the local topography at the surface. Within the middle hydrostratigraphic unit, hydraulic heads and fluid energies are highest at me basin edge to the east where the major aquifer of the unit is exposed, and much lower in the basin centre to the southwest where the aquifer is confined. The magnitude and distribution of fluid potentials in the two top hydraulic systems suggest that the general hydrodynamics of the basin are, to a large extent, responsible for the generation of the fluid pressures. In the third and deepest hydraulic system, however, the situation is different. The hydraulic heads and formation pressures are very high indeed, and cannot be explained purely in terms of circulating meteoric waters. Some other fluid energy sources must also be active in this part of the basin. The fluid potentials and pressures fluctuate very rapidly both laterally and vertically, suggesting the existence of distinct flow units within the entire system. Each flow unit appears to be hydraulically closed, sealed both vertically and horizontally, and characterized by a unique fluid energy distribution. The existence of both vertical and horizontal potential gradients at depth, especially at the basin centre, indicates that the fluids are not static, but mobile, and that the complex movement of fluids could be through deep-seated drains. Such fluid movements obviously affect the temperatures of the sedimentary layers and could also be significant in the migration and accumulation of hydrocarbons in the basin.