After all, such differences normally depend on the design and therefore translate into physical characteristics. More importantly, consumers in these markets may have compelling reasons, environmental or economic, to prefer energy or fuel efficient goods. Regulations and labelling programmes to do with energy efficiency and based on (few) international standards set by the International Electrotechnical Commission or the ones that follow closely the guidelines, methodologies and best practices developed by expert bodies such as the US-led Collaborative Labelling and Appliance Standards Programme (CLASP), and the APEC Energy Standards Information System (ESIS) are less likely to be challenged as unnecessary obstacles to trade within the meaning of the TBT Agreement.