The development of robust, comparable EEIs requires a coherent statistical foundation based on reliable energy-balance data. The ROK and Japan, whose national energy statistics follow the IEA's can be constructed with precision using legally mandated reporting systems, standardized calorific values, and detailed transformation-flow data. When extending this EEI development framework to ASEAN economies, several practical considerations emerge due to the distinct characteristics of ASEAN's energy systems, statistical capacity, and data availability. The following implications summarize how the APO EEI framework can be adapted and strengthened within the ASEAN context. Many ASEAN economies face persistent limitations in foundational commodity balance data. These include incomplete reporting of domestic production, inconsistent documentation of imports and exports, and substantial gaps in sector-level final consumption, especially in industry, transport, and noncommercial household sectors. For the APO's EEI methodology, which requires disaggregated information on energy flows by product and sector, improving the quality of the commodity balance is a prerequisite. ASEAN economies may therefore need to develop clearer reporting obligations, similar to the ROK's legally mandated statistical system, or adopt standardized templates, such as those used in the APEC-ASEAN joint questionnaire. Enhancing comparability of energy intensity measures across member economies. transformation processes, including power generation, refinery operations, coke production, accurate primary and final energy values. ASEAN economies, however, often lack such detail. CHP heat-electricity splits. Inconsistent or missing transformation data limit the ability to convert commodity balances into full energy balances, which, in turn, hampers the construction of thermodynamically consistent EEIs. Adopting simplified yet standardized transformation accounting rules, modeled on the Korean/Japanese frameworks, would significantly enhance the feasibility of EEI estimation in ASEAN economies. calorific values, particularly for biomass, waste fuels, and locally sourced solid fuels. For APO EEI calculations, where energy intensity must be measured in standardized units (e.g., toe, TJ), 148|APO PRODUCTIVITY OUTLOOK 2026|ENERGY EFFICIENCY, PRODUCTIVITY IMPACTS, AND COMPOSITE INDICATOR DEVELOPMENT