Experimental compaction of quartz sand was conducted in semistatic flow-through systems at 150°C to examine the chemical and physical processes associated with pressure solution. Pore-fluid chemistry and porosity were monitored through time to investigate the role of effective stress on silica solubility and compaction rate. The concentration of silica in the pore fluid varied directly with effective stress at constant pore-fluid pressure, but not in a linear fashion. Increases in silica were not transient and could be partially reversed by removal of the effective stress. Porosity decreased steadily under constant nonzero effective stress at 150°C, but remained essentially constant under identical loading conditions at room temperature. Initial compaction rates increased linearly with effective stress. Deformed samlpes show indented contacts with fractures and dissolution features, healed microfractures, and a decrease in average grain size. Multiple mechanisms (pressure solution, subcritical crack growth, crack healing) appear to operate at grain contacts during compaction. We interpret long-term, time-dependent compaction accompanied by stress-induced changes in fluid chemistry as evidence for pressure solution.