The 1993 SNA follows the Balance of Payments Manual in allowing for a single enterprise run as a seamless entity with substantial operations in two or more economic territories to be regarded as having a centre of economic interest in each of the countries where it is recognized by the tax and licensing authorities, but only when the activity is operating mobile equipment such as ships, aircraft and railways. In these cases, the possibility is for all the enterprise's transactions to be allocated to the countries of registry in proportion to the financial capital that the countries have contributed or their share of equity in the enterprise. Should this treatment be extended to other activities, for example hydro-electric schemes on border rivers and pipelines? Should reference be made to joint sovereignty zones and zones of joint jurisdiction?