The various processes involved in fluid flow and thermal energy transfer in major sedimentary basins are closely interrelated. The major thermal energy transfer processes appear to include conduction, convection by upward-moving pore fluids both on discrete and diffuse scales, and possibly endothermic or exothermic reactions. Fluid flow in sequences of accumulating sediments is predominantly the result of excess pressures. These excess pressures were probably produced by compaction disequilibrium and aquathermal pressuring. The latter is strongly temperature dependent as are several other secondary causes of excess pressuring. The combination of pressure-producing factors may create conditions for natural hydraulic fracturing and for subsequent pressure dissipation and up ard convection of heat. The pressure and temperature distributions in accumulating sedimentary basins are strongly dependent on (1) the thermal and hydraulic conductivities of the sediment, (2) the rate of sediment accumulation, and (3) the geothermal gradient.

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