Seven core samples from Leg 170 and 205 were used to measure vertical permeabilities of subsurface sediments from the Costa Rica margin (Table T1). The permeabilities of the pelagic carbonate sediments vary from ~4 x 10–16 to ~1 x 10–15 m2. The permeabilities of the hemipelagic mud sediments vary from ~2 x 10–18 to ~4 x 10–18 m2. All samples, viewed individually, show a decrease in permeability with decreasing porosity (Fig. F3). Viewed as a group, the pelagic carbonate samples show no trend, whereas the hemipelagic muds show a possible overall decrease in permeability with decreasing porosity. Tests at lower porosities (McKiernan and Saffer, this volume) support this trend. Table T2 summarizes the results of the grain-size, total inorganic, and total organic carbon analyses. Hemipelagic mud samples average 60 wt% clay-size, 37 wt% silt-size, and 3 wt% sand-size grains, and carbonate percentage is low (averaging ~4 wt%). Pelagic carbonate samples average 53 wt% silt-size, 45 wt% clay-size, and 3 wt% sand-size grains, and carbonate percentage is high (averaging ~62 wt%).