According to Telegraph (an account is required to read the whole article), Gazprom seemed to have created an important pressure by using different gas prices for different EU countries:
Vladimir Putin’s abusive stranglehold over European gas supplies has been laid bare by explosive EU documents, exposing deliberate violations of EU law and a pattern of political bullying over almost a decade.
The longest investigation in EU history found that the Kremlin-controlled energy giant Gazprom has used its enormous power to pressure vulnerable states in Eastern Europe, and to fragment the EU’s unified energy market with coercive pricing policies.
The report suggests that Germany has been enjoying a sweetheart deal with Gazprom, gaining a competitive advantage in gas costs at the expense of fellow EU economies and leaving front line states at the mercy of Moscow's strong-arm tactics.
However, Gazprom's policy of quite different gas prices for different countries is not a surprise (e.g.):
Romania pays the highest price in the area for natural gas and the fourth in the European Union and the only source of gas is Russia’s Gazprom, European Commission’s DG Energy report shows.
This article seem to confirm the alleged good prices for Germany:
Gazprom’s average European gas price was $182.50/1,000 cu m in the first half of 2016, Gazprom’s average price for 2016 is estimated at around $165-$170/1,000 cm. (..) Germany gets most of its gas from Russia, went as low as $145/1000 cm($4/MMbtu) or about 20% less than the spot price at the UK NBP hub.
Note: The same article argues that the exact prices for European countries is not known, so it is unclear how the first sources got their data:
Gazprom does not disclose the prices it charges its European clients, only an average price charged for its European customers.
Question: Why does EU Commission seem to allow quite different Russia gas prices for EU members?