This study aims to determine the effectiveness and ability of water hyacinth (Eichornia crassipes Mart. Solm) in reducing COD and BOD levels in petroleum liquid waste. Petroleum liquid waste is one type of waste that pollutes the environment if it is not treated first. In this study, biological treatment techniques were carried out using phytoremediation techniques. Phytoremediation is an effort to reduce and improve the quality of waste by using plant agents so that the levels of pollutants contained in the waste can be reduced. Phytoremediation techniques are carried out using a simple bioreactor with various concentrations of petroleum liquid waste, namely control (0% waste), 10% waste, 20% waste, and 30% waste. The results of this study showed that the water hyacinth plant was able to tolerate liquid petroleum waste, which was indicated by the water hyacinth plant being able to survive up to a concentration of 30% for approximately 2 months. Based on the measurement of BOD and COD of petroleum liquid waste before phytoremediation was carried out, it was 20 mg/l and 10.04 mg/l, respectively. At 10% effluent concentration, the BOD and COD values decreased to 4.11 mg/l and 14.7 mg/l. At 20% effluent concentration, the BOD and COD values also showed a decrease to 3.73 mg/l and 9.14 mg/l. At 30% effluent concentration the BOD and COD values showed a decrease to 3.73 mg/l and 1.22 mg/l. The ability of the water hyacinth plant to reduce BOD and COD values can show its effectiveness to be used as a phytoremediation agent for petroleum waste.