The EU is hastening to sign new contracts with Azerbaijan, moving the gas via a pipeline across Turkey to Southern Europe. Gas might also someday come from farther afield in Central Asia. Turkmenistan has built a pipeline to the Caspian Sea. An underwater pipeline across the Caspian could bring that gas to the Azerbaijan network.

Perhaps the most dangerous point of vulnerability is within the German network itself. Gas is pushed through pipelines under pressure. If the network doesn’t contain enough gas, the pressure drops and the gas cannot move. A big enough shortfall going into the pipe can translate into a 100 percent shortage at the other end. So any rationing plan is likely to be very unequal: In order to sustain pressure in high-priority pipes, the gas may have to be turned off altogether to lower-priority pipes.

The political risks of the decisions here are obviously high. Put industry before consumers? Electricity before heating? Big cities before small towns?

Another agonizing dilemma: Much of German industrial production is outsourced to nearby EU partners—Hungary and Slovakia especially. Those countries depend even more on Russian gas than Germany does. How much of Germany’s gas should be shared with them?