Abstract
As a result of the growing digitization of society and the development of electronic economy, current statistical data sources, including administrative registers, do not satisfy the information needs of society. Therefore, there are growing gaps in the statistical coverage of a number of sectors of the economy. One example of such a gap is the secondary real estate market, which is only partially accounted for by official statistical data sources. On the other hand new data sources such as the Internet or Big Data tend to decrease information gap in official statistics. The Web portals that specialise in brokerage on real estate market should be not neglected as a data source for statistics. Therefore, the aim of the paper is to use two Web portals devoted to the housing market to estimate supply measured in the number of flats offered to sale in Poznań, Poland. In addition, classification and quality of Web portals will be discussed.