Barriers to entry can cause differences between ''legal'' and ''economic'' degrees of market openness. The German electricity market is legally 100% open. The industrial segment is also close to being economically 100% open. The general pattern indicates a mature market. However, the domestic segment is economically only 61% open. Possible explanations of this difference from its legal openness are mismatch of regulation and market strategies of incumbents. For the total market, the economic degree of market openness is 89% based on volumes. It is 61% based on customer numbers, reflecting the fact that the vast majority of customers are domestic.