The main GATS principles are most favoured nation (MFN), market access and national treatment. Based on these basic principles, WTO members make commitments specific to the service sectors and sub-sectors listed in their country's schedule. Hence the extent and conditions under which the basic principles of GATS apply to individual service sectors in any country, can be assessed only by referring to that country's schedule, the character of the existing regulatory regime and the nature of the limitations, if any, to which the commitments are subject. The schedules cover 12 sectors (business, including professional and computer services; communication services; construction and engineering services; environmental services; financial services; health services; tourism and travel services; recreational, cultural and sporting services; transport services; and other services not included elsewhere), and 155 sub-sectors. The commitments are further listed according to the four modes in which service trade takes place: (1) cross-border movement of service products; (2) movement of consumers to the country of importation; (3) the establishment of a commercial presence in the country where the service is to be provided; (4) temporary movement of natural persons to another country in order to provide the service there.
By including a service sector or sub-sector in its national schedule, a country indicates that it will apply market access and national treatment obligations to trade in the sector. It is, however, open to a country to indicate the limitations under which it will grant market access or national treatment for each of the modes in which international trade in services takes place. Such restrictions could be horizontal, covering the entire range of services; or specific to the sector or activity in question.
Assessed in terms of partial liberalisation of services there is evidence of developed countries accepting some cross-border access in more than two thirds of sectors, and some form of commercial presence in almost all sectors. Developing countries have allowed some form of cross-border market access in about 25 per cent of instances, allowing some foreign commercial presence and some dimensions of national treatment for foreign establishments in about one third of the tabulated instances. Barriers to trade in services are less transparent and measurable than those applied to goods trade. However, empirical work in 1999 indicates that trade barriers in services remain significant, and that the economic gains from further liberalisation of trade in services would be substantial.
The areas where the impacts of liberalization might be felt more quickly in developing countries is in services. On the one hand liberalisation in developing countries might facilitate improved market access in developing countries for financial institutions and telecommunications suppliers, with consequential economic gains in improved efficiency of lower prices. On the other hand, liberalisation of the industrial countries might allow better access for labour-intensive construction and transport services from the developing countries. Also, developing countries may be able to obtain 'more value for money' thereby releasing resources for other policy goals.