Summer and winter depth distributions of Ar, N2, CH4, total CO2, and total H2S were obtained at two stations in Chesapeake Bay. The data indicate that CH4 escapes the sediments as bubbles, stripping Ar and N2 from the sediments. Total CO2 increases to concentrations greater than 1,000 milliliters per liter with depth and pH remains constant at about 7. Low and uniform total H2S concentrations indicate removal of sulfur as iron sulfides. The absence of CH4 in the upper 25 centimeters of these sediments and the presence of Ar and N2 in concentrations similar to the overlying water indicate mixing to at least this depth.