For instance, Tier One in the EU-United States proposal covers energy-related services (e.g. engineering and maintenance services to optimize the environmental performance of energy facilities), and services for the design and construction of energy-efficient buildings and facilities. Tier Two covers a broad set of environmental and climate-related services, including energy, construction, architectural, engineering and integrated engineering services.45 Once the picture on the services front is sufficiently clear, the negotiators would proceed to identify the goods essential to the delivery of the selected environmental and energy services and negotiate tariff concessions using the proposed modalities and taking into account national priorities and programmes. The introduction of sustainability standards and regulations may prove important to trade in biofuels.