The paper reviews and meta-analyzes 59 studies on the biological treatment of oil and gas produced water, highlighting its potential for recycling and beneficial reuse. Physical-chemical treatment methods have traditionally been favored due to their space efficiency and simplicity, but changing regulations and the need for water recycling have led to increased interest in biological treatment. The studies, conducted from 1979 to 2018, used real and synthetic produced water samples, with China and the USA being the primary sources of real samples. Most studies (69%) were bench-scale experiments, and fixed-film reactors were the most common treatment configuration (32%). The median total dissolved solids (TDS) and chemical oxygen demand (COD) of treated waters were 28,000 mg L⁻¹ and 1125 mg L⁻¹, respectively. Inhibition by salinity varied, but efficacy generally decreased when TDS exceeded 50,000 mg L⁻¹. For real samples, average COD removal was 73% when TDS was below 50,000 mg L⁻¹ and 54% when TDS was above 50,000 mg L⁻¹. Key issues included microbial acclimation, toxicity, biological fouling, and mineral scaling. The paper concludes that biological treatment is promising for producing effluents suitable for reuse, especially when integrated into larger treatment trains.The paper reviews and meta-analyzes 59 studies on the biological treatment of oil and gas produced water, highlighting its potential for recycling and beneficial reuse. Physical-chemical treatment methods have traditionally been favored due to their space efficiency and simplicity, but changing regulations and the need for water recycling have led to increased interest in biological treatment. The studies, conducted from 1979 to 2018, used real and synthetic produced water samples, with China and the USA being the primary sources of real samples. Most studies (69%) were bench-scale experiments, and fixed-film reactors were the most common treatment configuration (32%). The median total dissolved solids (TDS) and chemical oxygen demand (COD) of treated waters were 28,000 mg L⁻¹ and 1125 mg L⁻¹, respectively. Inhibition by salinity varied, but efficacy generally decreased when TDS exceeded 50,000 mg L⁻¹. For real samples, average COD removal was 73% when TDS was below 50,000 mg L⁻¹ and 54% when TDS was above 50,000 mg L⁻¹. Key issues included microbial acclimation, toxicity, biological fouling, and mineral scaling. The paper concludes that biological treatment is promising for producing effluents suitable for reuse, especially when integrated into larger treatment trains.