The typical service lives of operational energy pipelines are up to 50–70 years. The existing lines would subsequently be decommissioned and replaced with new lines. As one approach to dealing with a decommissioned line is by leaving the line untouched in the ground, there exists uncertainty in the structural integrity of decommissioned lines under external corrosion over time. This paper introduces reliability-based integrity assessment of decommissioned pipelines that remain in the ground. Two limit state functions are developed to quantify (i) formation of perforations under pitting corrosion, and (ii) thinning of pipe wall thickness under uniform corrosion and initiation of pipe yielding under soil and traffic loading. Corrosion occurrence and growth are modeled as stochastic processes to account for its spatio-temporal uncertainty. The reliability and safe remaining lifetime of an entire pipeline sections are determined using enhanced Monto-Carlo simulations. A sensitivity analysis is performed to identify the governing factors of the life expectancy. The proposed integrity assessment is illustrated on an example.