Measurements of the background concentrations of nutrients, dissolved oxygen (DO), and salinity were obtained from a beach that has oil from the Exxon Valdez oil spill in 1989. Two transects were set across the beach, one passed through an oil patch while the other transect was clean. Three pits were dug in each transect, and they ranged in depth from 0.9 to 1.5 m. The DO was around 1.0 mg L(-1) at oiled pits and larger than 5 mg L(-1) at clean pits. The average nutrient concentrations in the beach were 0.39 mg-N L(-1) and 0.020 mg-P L(-1). Both concentrations are lower than optimal values for oil biodegradation (2 to 10 mg-N L(-1) and 0.40 to 2.0 mg-P L(-1)), which suggests that they are both limiting factors for biodegradation. The lowest nitrate and DO values were found in the oiled pits, leading to the conclusion that microbial oil consumption was probably occurring under anoxic conditions and was associated to denitrification. We present evidence that the oxygen level may be a major factor limiting oil biodegradation in the beaches.