23.1. Introduction. The present chapter discusses the problem of identifying and recording trade in ships and aircraft and indicates the means through which this trade can be captured in an internationally comparable way. Possible data sources are discussed, as well as the issue of leasing. The available data indicate that there is a need to improve the statistical recording of ships and aircraft. This chapter is linked with chapter XX as the refitting of a ship or aircraft can be viewed as a good for processing. The compilation of data on trade in aircraft and ships frequently requires the use of non-customs sources. Therefore, this chapter is linked with chapters III and IV, on the use of non-customs sources of data, and also with chapter VII, which discusses the integration of data from different sources.
 Rigs for oil production might be included in this category of goods as well. For example, in the European Union, transactions in oil rigs are treated in the same way as transactions in vessels if these structures are floating as opposed to being fixed. For the treatment of fixed installations or installations in general, see para. 6.8.
 For 2009, countries reported collectively US 141 billion in exports of ships (Standard International Trade Classification (SITC) section 793) but only US 57 billion in imports. While trade has increased dramatically, this pattern has persisted for many years. The registration of ships under so called flags of convenience in a limited number of relatively small countries appears to be a major reason why imports are underreported globally. Some of these countries do not report their trade data internationally. However, if the registration of ships is open to owners that are not resident in these countries those ships registered under foreign owner should not be included in their trade statistics in any case. For 2009, countries reported over 41 billion in exports of ships (SITC group 793) to only three countries: Panama, Marshall Islands and Liberia, which either do not show any such imports or do not report trade data. The worldwide trade in aircraft (SITC group 792) shows global exports as having systematically exceeded imports by a wide margin until 2008, but the margin was not as large as that for ships (the figure for exports for 2009 was distorted owing to the lack of detailed commodity reporting of a major exporting country). See 2009 International Trade Statistics Yearbook, vol. II, Trade by Commodity (United Nations publication, Sales No.E.II.XVII.3H). Available from http://comtrade.un.org/pb/.