Decommissioning of offshore structures is not a novel issue in the oil and gas industry. Malaysia is now dealing with a fleet of ageing platforms slated to be decommissioned. There are several alternatives of decommissioning such as "complete removal" and conversion to artificial reefs; "partial removal", "remote reefing" and "topple in-situ". Given the list of options, the decision to undertake the best option is challenging as the current method of comparative Best Practicable Environmental Option (BPEO) assessment is only implemented at the end of platform's life. Therefore, the main goal is to develop a management decision making tool which is incorporated throughout the life cycle of an oil field. Expert elicitation is conducted to verify the relevant decommissioning criteria. The criteria were then ranked accordingly through calculation of Relative Importance Index (RII), and a conceptual system is established to complement the existing asset management system. In summary, this study could benefit the knowledge of offshore decommissioning planning through prioritization of decommissioning criteria. © (2014) Trans Tech Publications, Switzerland.