提升能源效率是減少溫室氣體排放議題中至為關鍵的策略之一，大多數國家都以能源生產力衡量總體層級的能源效率，在運用時未曾細究此一指標的經濟內涵與適用性，直至2008年12月的第十四屆締約國會議（Fourteenth Session of the Conference of the Parties, COP14）中，聯合國氣候變化綱要公約（United Nations Framework Convention on Climate Change, UNFCCC）首度呼籲各國重視能源效率的衡量問題。本文指出，傳統的能源生產力指標因受多種與使用技術及配置效率無關之他種因素的影響，並不適合用做為衡量能源效率的指標，而只適合衡量為達特定實質國內生產毛額（gross domestic product, GDP）水準的能源成本有效性。本文也同時檢討技術效率及相關指標的問題，並提出一個新的能源效率指標，除可避免其他指標可能出現的不一致性問題之外，亦可反映缺乏效率的來源、以及廠商在不同環境政策工具下的能源效率差異，並用以評估外生變數變動對能源效率的影響。

Improving energy efficiency is one of the critical strategies to reduce greenhouse gas (GHG) emissions. Energy productivity, as an indicator of energy efficiency, is pervasively used worldwide. However, United Nations Framework Convention on Climate Change (UNFCCC) in Fourteenth session of the Conference of the Parties (COP14) has noted that the economic meanings and suitability of this indicator need to be explored. This paper points out that the traditional energy productivity could measure only the cost effectiveness of energy in order to achieve a given level of real gross domestic product (GDP), but not the energy efficiency "per se". After critically reviewing a number of existing indicators, I propose a new one and show its difference from energy productivity and other indicators which may cause inconsistency between technical efficiency and cost efficiency. Furthermore, the origins of the inefficiency can be decomposed and in response to alternative environmental regimes.