 to the following conclusions. Firstly, it seems that all the hypothesized types of M&A transactions were found from the year 2001 to the year 2007. Secondly, the years 2004 and especially 2005 were active ones in terms of total number of transactions. While the revenue data also shows that the total volume of the OSS market increased from 100 % horizontal entry expansion strengthening Fig. 6 The percentage and number of types of M&A transactions in the OSS market L. Frank et al. 2002 to 2005 over 30% from USD21.2 billion to USD27.6 billion (based on Dittberner data), indicating that the market was then at the adoption and transition phase, high M&A activity would signify a fierce battle for market shares. Regarding the percentages of different transaction types, it seems that a major share of the transactions belongs to the strengthening category, although the trend is descending. While the share of expansion mergers and acquisitions remains approximately the same throughout the years, the horizontal entry transactions first occurred in 2004 and the percentage of that type is increasing. This would also indicate that the software market is in the third phase of its evolution. The entry of horizontal software providers to the OSS market is likely to have a major impact on the competition and further evolution of the market. What is interesting is that Oracle has strongly inclined towards the OSS market during the analyzed term and, having bought five OSS software vendors, gained a stable market position on several OSS market segments. The conclusion of the study, however, is that both cases, where merger or acquisition was committed to strengthen current market position and to enter new segments or vertical software markets, were found. This notion is treated as an indication of increasing horizontalization of the market. Altogether, further analysis is still needed. The next chapter aims at clarifying the reasons of the observations by analyzing the reasons related to the special features of software business an