This study examines the deviation of concentration from its steady state level in Iranian manufacturing industries. The study is carried out for 94 industries based on cross- section method with four-digit ISIC code in the years 1999 and 2007. The coefficient of partial adjustment is significant and less than one. Therefore there is significant partial adjustment towards steady state level of concentration.The same results were obtained in subsamples including 47 industries with high advertising intensity and 47 industries with low advertising intensity. The comparison of Herfindahl Hirschman index indicates that the level of industrial concentration in the majority of industries (63 percent) has decreased during this period. The findings of the study support the Sutton the market size in exogenous sunk cost industries. But the result is not valid for endogenous sunk cost industries.

The importance of market concentration for government decisions and policies to regulate the market is inevitable. In this study, market indexes were calculated to identify the market status of particleboard imports and to help industry practitioners to identify the particleboard market and identify production potential. In this study, the market structure was measured using concentration ratios, Herfindahl-Hirschman, Hall Tideman, Comprehensive Industrial Concentration, and Hannah-Kay. The market structure was measured for the period 2010-2019. According to the calculations, the average concentration ratio of the four major exporting countries to Iran for the ten-year period studied was 97. 81% of the total import of particle board to the country. They indicates a market with a multilateral monopoly. Other indicators include the Herfindahl-Hirschman index at 5, 561, the Hall Tideman index at 0. 54, the Comprehensive Industrial Concentration Index at 0. 79, and the Hall Tideman Index at α value of 0. 6 to 3. 12, α value was equal to 1. 5, to 2. 27 and α value was equal to 2. 5 to 2. 02. The results have shown that the market situation on the import of paticle board was the multilateral monopoly. The status of this monopoly has fluctuated and changed over the past ten years due to the political and economic decisions of governments and the change in domestic production of particleboard. In this market situation, exporting countries can argue over price and export rates. Turkey, United Arab Emirates, Thailand, Italy and Russia has been Iran's most important trading partner in the particleboard import market during the period under review, with the most imports being indexed to these countries, indicating a multilateral monopoly.