Russian energy company Gazprom said it was considering \"proactive\" measures to ensure its consumers meet contractual obligations. Gazprom said it was normal for consumers to take on less natural gas than contracts stipulate. Excessive gas then settles in a gas transmission system. \"This hinders the fulfillment of requests from independent producers for gas transmission to other purchasers,\" Gazprom said. \"In the end, such a situation keeps down the development of the Russian gas market which stipulates the flexibility of transmission services.\" Many of Gazprom\'s contracts include \"take-or-pay\" clauses, meaning downstream markets are liable for natural gas they might not use. \"Proactive steps should be taken to improve the regulatory framework in this area, particularly by introducing the GTS users\' liability for fulfilling their contractual obligations,\" the company said. Ukraine is contesting a $7 billion bill sent by Gazprom for unused gas from last year. Kiev has moved for relief from its energy ties with Russia. It says a 2009 natural gas deal is too expensive when compared with other European contracts. In September, the European Commission announced an investigation into Gazprom\'s activity in the eurozone. The commission said it was concerned that Gazprom abused its market position in the upstream natural gas sector in Central and Eastern Europe.