The matenal IS subjected to correction by the author. Permission to copy IS restricted to an abstract of not more than 300 words Write: 6200 N. Central Expwy., Dallas, Texas 75206. ' Earlier work has shown that the addition of sodium silicates to dilute surfactant systems reduces surfactant retention in Berea cores better than Na2C03, NaOH or STPP. This paper addresses the fact that in solution the sodium silicate molecule is a complex mixture of species which can exhibit a variety of properties, depending on the concentration and ratio of Si0 2 to Na02' By selecting the specific form in which the sodium silicate is added, it is possible to optimize the recovery of oil under a 'broad range of reservoir conditions. Specific variables which may be affected by silicate chemistry are 1FT, rock wettability, surfactant retention and specific permeability reduction, leading to improved three-dimensional sweep.A series of dilute surfactant core flooding tests were carried out, both with and without oil present, to determine the concentrations of the injected chemicals in the effluents. These tests covered a range of silicate ratios, brine salinity and hardness levels, and temperature conditions. The results show that each of these variables has specific effects on the retention of the injected chemicals by the sandstone substrate. Specifically, hardness increases retention of both silicate anion and surfactant, even with a large, soft water preflush. However, the silicate anion is preferentially retained, thereby leaving more surfactant in solution. Higher temperatures decrease retention of the surfactant and silicate anions. These results relate to observations of changes in recovery efficiency and permeability.