Description: Advances in the development of petroleum resources has contributed enormously to the global energy demand and economic development over the past decades, however, it has left profound negative impacts on the natural environment and adverse human health effects in most oil-producing host communities around the world. Apart from the loss of petroleum-derived revenue to corruption and ineffective government's petroleum development policies, the Niger Delta region has experienced a wide range of environmental pollution, degradation, human health risks and socio-economic problems associated with petroleum exploration, development and production. Over the years, several environmental laws have been institutionalized to regulate the petroleum sector in Nigeria. The Nigerian government and other African countries have played tremendous roles in the emergence of international environmental law that regulate the establishment of environmental institutions and legislations as well as strategies for conservation and management of natural resources. However, the existing Nigeria statutory laws and regulations for environmental protection appear to be grossly inadequate and some of the multinational oil companies operating in the Niger Delta region have failed to adopt sustainable practices to prevent environmental pollution. Poor implementation of national and international environmental policies associated with petroleum exploitation and production in the Niger Delta region have resulted in huge environmental costs, degradation and issues of responsibilities from the oil companies. Therefore, this research paper examines some of the contributions of multinational oil companies operation towards environmental degradation and the role of Nigerian Government in the implementation of the petroleum-related environmental policies in the Niger Delta region.