Nigeria faces environmental and safety risks due to poorly implemented decommissioning of aging oil pipelines. This study addresses critical gaps in technical practices and regulatory enforcement by developing an integrated implementation strategy for Nigeria. Systematic failures were revealed by combining field surveys, laboratory analysis. The study reveals that sixty percent of pipelines older than 25 years were left in place without flushing, leading to soil contamination. In response, a novel three-phase decommissioning model is suggested, Phase 1 mandates integrity checks and community consultation, Phase 2 requires pipeline flushing, segment removal, or inert filling, and Phase 3 enforces pre/post-environmental impact assessments (EIA) and public disclosure. This framework, which is in line with international standard, distinctively takes into account the socio-ecological characteristics of Nigeria. This paper also emphasized the necessity of immediate legislative changes and suggests a national decommissioning code, EIAs with third-party verification, and inter-agency cooperation. This strategy provides a scalable model for resource-dependent economies.