Since the classical economics, the model of competitive advantage at different levels (national, industry, firm) has been considered attentively by experts in economics and management. In recent years, one pivotal issue in the field of management has been the identification of competitive advantage sources and the breakthrough strategies for its preservation and development. The main purpose of this article is to explain one of the popular theories concerning the competitive advantage model, that is Porter's model, to show whether it is applicable in a country like Iran, which possesses a highly dominant government-based economy, or not. Besides, if it requires any modification in its pattern, what form of modification should it comprise? In terms of methodology, thus, this may be deemed an applied developmental research. Primary data targeted was obtained by means of a quantitative survey using a questionnaire technique of data collection. The questionnaire survey took place in the period from 10/2010 to 6/2011 and a total of 109 firms (undertaking their activities in the territory of the Iran) were involved. The results of the study show that Porter's model in both the upstream and the downstream forms must become developed and rectified. Ultimately, the most advantageous shape of the model for detecting the sources of competitive advantage in bottled drinking water industry is offered.

The paper is an examination of Balassa's 'revealed comparative advantage' (RCA). The results of researches show that when using the RCA, it should always be attuned in such a way, that it becomes symmetric.This paper consists of three major parts i.e. theory, analytical tool and case studies of comparative advantage. First we evaluate the theory and various empirical measures. Then this analytical tool is applied to analyze exported product. The results indicate that Iran had not comparative advantage in export of walnut, almond hazelnut, apple, orange. To increase competitiveness, we suggest several policy recommendations such as increasing agricultural productivity, promoting the development of indigenous technological capabilities, and reducing the cost of doing business. The conclusion is based on a theoretical discussion of the properties of the measure, and on convincing empirical evidence, according to the Balassa index.The index for 2007 shows that Iran does not have a comparative advantage in export of walnut, almond hazelnut, apple and orange and reduced its market share in these products.