Oil industry activities often involve the cleaning and replacement of pipelines, usually resulting in the discharge of effluents into waterbodies. The toxicity of de-oiling effluent from a decommissioned crude oil pipeline in the Niger Delta region of Nigeria was assessed using the brackish water shrimp Palaemonetes africanus in a 96 h laboratory bioassay. On the basis of the computed 96 h LC 50 , the effluent showed a significant dose-dependent relationship in its toxicity between 24 and 96 h of exposure. The 96 h LC 50 was 4.6 times more toxic than the 24 h LC 50 , indicating that the toxicity of the effluent increased over the study period. Besides crude oil and refined petroleum products, which are often the major concern for regulators, there is a need for the proper enforcement of standards and safe limits for effluents prior to discharge so as to protect sensitive marine species.