ABSTRACT The role of water in petroleum migration has hitherto been grossly underplayed because of the unsuccessful search for a model that demonstrates the movement of water and hydrocarbons combined in a single phase, It appears, however, that many of the alternative mechanisms that have been favoured also require the availability and movement of large quantities of water at great depths for their efficiency. For example in models that favour continuous oil phase during migration, excessive pore pressures required to overcome capillary pressures can be enhanced at depth in thick sedimentary basins by one form of "aquapressuring" or the other. The release of diagenetic water can therefore induce petroleum migration if it takes place at burial depths where temperatures are high enough for organic maturation. The extent of clay dewatering in the Lower Benue Trough was semiquantitatively evaluated .here bv monitorine the steowise chanee in the lattice soacine of montmorillonite and mixedlayer frays with bugal. A mddel derived-from the analyses$howsthat as much as 36 Million hl3 of clav lattice water oer M3 is released at de~ths where oraamc maturation has been ach~eved. The mddel also shows ihat as much as 2 million M3 of crude oil could have been released Into intrastratified resewoir rocks from every 1 lolometer mterval of shale in the ham by solution mechmisms a1one;probably much more though other pore water-related processes.