The combined market share of the four electricity suppliers with the largest market shares (“concentration ratio” – CR) in a year indicates how market shares are distributed in the electricity retail markets. The Bundeskartellamt makes a distinction between two defined markets: a national market for the supply of electricity to interval-metered customers and a national market for the supply of electricity to standard load profile customers on special contracts (non-default contracts and excluding heating electricity). The distribution of the market shares among the players in a particular market determines the degree of market concentration, which can be used to identify potential market power.

For the purposes of the monitoring reports, the suppliers’ sales volumes are collected as the national totals for each individual company (legal entity). The figures for the individual companies are used to calculate the sales of the four suppliers with the highest sales volumes in each market segment in a year. The four suppliers with the highest sales of electricity are not necessarily the same each year. The sales volumes are aggregated using what is known as the dominance method: if one supplier holds at least 50% of the shares in another supplier, the suppliers’ sales volumes are added together.