Nigeria’s oil and gas industry remains central to national economic development, revenue generation and energy supply, but petroleum exploration and production have also produced persistent environmental challenges, particularly in the Niger Delta. Oil spills, hydrocarbon contamination of soil and water, gas flaring, ecosystem degradation, petroleum waste, biodiversity loss and the environmental consequences of crude-oil theft and illegal refining continue to affect ecological integrity, public health and community livelihoods. This article critically examines the legal and institutional framework governing environmental protection in Nigeria’s oil and gas sector, with particular attention to the Petroleum Industry Act 2021, the Environmental Impact Assessment Act, the National Oil Spill Detection and Response Agency Act, the National Environmental Standards and Regulations Enforcement Agency Act and relevant subsidiary regulations. It evaluates the respective environmental responsibilities of the Nigerian Upstream Petroleum Regulatory Commission, the Nigerian Midstream and Downstream Petroleum Regulatory Authority and other relevant institutions, focusing on institutional coordination, enforcement, remediation, financial responsibility and access to environmental justice. The study adopts a doctrinal and comparative methodology, complemented by relevant empirical and institutional evidence. Comparative perspectives from Norway, the United States and Ghana are examined to identify regulatory approaches capable of strengthening Nigeria’s environmental governance. The article finds that Nigeria possesses a substantial legal and institutional framework, but significant gaps remain between legal prescription and environmental outcomes. It therefore recommends stronger institutional coordination, continuous environmental monitoring, transparent enforcement, adequate remediation financing, independent verification of restoration and meaningful community participation. Keywords: Environmental Governance; Oil and Gas; Environmental Pollution; Niger Delta; Petroleum Regulation; Environmental Remediation.