Russia's Gazprom on April 23 served Ukraine's Naftogaz with a bill of $11.388 billion, representing a penalty for the shortfall in gas purchases under pay-or-take terms in 2013, Gazprom Deputy CEO Alexander Medvedev told reporters.

The contract stated that Naftogaz should have bought 41.6 billion cubic meters of gas, but it only took 12.9 bcm.