In this paper I treat some leading rulings on compensation and reparation in the jurisprudence of international investment arbitrations, for the purpose of clarifying the trend of judgment upon the damage valuation criteria and methods. The recent discussion on the investment arbitration cases puts too much emphasis on various standards in substantive law, for example, expropriation, fair and equitable treatment obligation, most-favored-nation treatment obligation, and national treatment obligation. However, it is obviously the result of calculation of compensation or reparation that determines the success or failure of the investment arbitration system, and on such basis we have to evaluate whether or not the investment arbitrations perform effectively. In effect, many controversies on the substantive law, for example distinction between the expropriation and the fair and equitable treatment obligation, would eventually be transformed into the problem of whether their valuation criteria could differ or not. In this sense, the process of damages evaluation plays an important role in maintaining the balance of system in the international investment law as a whole. On the other hand, is it possible to derive generally applicable criteria for the ruling of compensation and reparation, while these are significantly influenced by particular circumstances of each case? In this regard, the following two points have been widely recognized as premises in the international investment law. In the first place, concerning expropriation measures, "reparation" amounts are normally larger than "compensation" amounts. Secondly, reparation costs more in cases of "expropriation" than that of "non-expropriation". It is the very purpose of this paper to re-examine these two premises. Firstly, while confirming the significance of the theoretical distinction between the notion of compensation and that of reparation, I point out that their valuation methods and results are identical in the practical point of view (Section I). Secondly, I am going to indicate that the recent jurisprudence does not follow the clear distinction between the expropriation case and non-expropriation one with regard to their calculation phases. I will conclude that the decisive factor for the classification of cases is whether or not there has been "a total loss" of investment assets (Section II). On the basis of the examination above, I derive finally some policy implications.