Encapsulated cell bioaugmentation is a novel alternative solution to in situ bioremediation of contaminated aquifers. This study was conducted to evaluate the feasibility of such a remediation strategy based on the performance of encapsulated cells in the biodegradation of gasoline, a major groundwater contaminant. An enriched bacterial consortium, isolated from a gasoline-polluted site, was encapsulated in gellan gum microbeads (16-53 mum diameter). The capacity of the encapsulated cells to degrade gasoline under aerobic conditions was evaluated in comparison with free (non-encapsulated) cells. Encapsulated cells (2.6 mg(cells) g(-1) bead) degraded over 90% gasoline hydrocarbons (initial concentration 50-600 mg L-1) within 5-10 days at 10degreesC. Equivalent levels of free cells removed comparable amounts of gasoline (initial concentration 50-400 mg L-1) within the same period but required up to 30 days to degrade the highest level of gasoline tested (600 mg L-1). Free cells exhibited a lag phase in biodegradation, which increased from 1 to 6 days with an increase in gasoline concentration (200-600 mg L-1). Encapsulation provided cells with a protective barrier against toxic hydrocarbons, eliminating the adaptation period required by free cells. The reduction of encapsulated cell mass loading from 2.6 to 1.0 mg(cells) g(-1) bead caused a substantial decrease in the extent of biodegradation within a 30-day incubation period. Encapsulated cells dispersed within the porous soil matrix of saturated soil microcosms demonstrated a reduced performance in the removal of gasoline (initial concentrations of 400 and 600 mg L-1), removing 30-50% gasoline hydrocarbons compared to 40-60% by free cells within 21 days of incubation. The results of this study suggest that gellan gum-encapsulated bacterial cells have the potential to be used for biodegradation of gasoline hydrocarbons in aqueous systems.