In connection with the spread of globalisation, liberalisation and deregulation of international financial markets as well as due to the progress of IT, the number of mergers and take-overs in the banking sector is seen to be growing. The aim of this survey is to present the influence of such events on the efficiency in the Polish banking sector, in the years 1997-2001. The efficiency measurement assumed here is technical efficiency; the returns according to the scaled and non-parametric Malmquist productivity index.

In order to examine the technical efficiency and returns to scale the author used Data Envelopment Analysis (DEA), which is a method developed in 1978 by three American scientists A. Charnes, W. Cooper and A. Rhodes. It is a determinist method, which assumes that there is no random component and which does not require functional dependence between input and output. The authors of the DEA method used the productivity concept, formulated by Debreu (1951) and Farrel (1957) which defines the productivity measure as the ratio of a single virtual output to a single virtual input. They applied it to a multidimensional situation in which there can be more than one input and more than one output.

The results of the survey reveal that mergers and take-over processes have stimulated efficiency and productivity growth in the banking sector. One of the most important conclusions of the survey is the fact that all the banks participating in these processes have significantly increased their efficiency and productivity indices. Size is the main factor which influences the efficiency of the banks analysed. Most of the efficient banks in the Polish banking sector are those which belong to a group of "very big" banks, while most of the least efficient banks are the "small" ones. The results of the analysis also demonstrate that the technical inefficiency and low returns to scale result from the still too numerous "small" banks which are unable to attain a better input to output ratio because their expenditures are too low. The results of the survey with regard to mergers and take-overs in the commercial banking sector allow the forming of a conclusion that this process should be continued and it should also include the "small" and "medium-size" banks, because there are still too many inefficient banks.