The efficiency of external commerce operations constitutes a result of many factors. The problem of the efficiency of investments in products/services for export, in principle, does not differ from the problem of investments in general. In all cases the efficiency of investments is reduced to the obtained effect: the volume of production, the net income, the economy of the living, materialized labour force. The efficiency of investments, in a country with an open economy, as for example Moldova and Romania,present a series of specific elements: the current annual expenditures are determined by the impact of the prices for raw materials, goods, the final product, which are allied quantities. Thus the component indicators in the calculation of the economic efficiency of the investments will have certain values with a certain probability, will vary. In this context, the calculations will be done as mathematic expectations of the indicators; here appears the necessity to determine the variations of the indicators.