OAO Gazprom (GAZP) , the world’s largest natural gas exporter, may face the biggest decline in European gas revenue in five years as demand weakens and buyers negotiate discounts, according to two company officials. Sales to the European Union, the source of 40 percent of revenue by Russian accounting standards, are forecast to fall more than 10 percent to about $55 billion this year, said the officials, asking not to be identified as the forecast isn’t public yet. Gazprom’s press service declined to comment. The forecast doesn’t take into account the rift between the EU and Russia over its involvement in the crisis in Ukraine , the main transit route for gas to Europe . While flows so far remain unaffected, the EU is seeking to ease reliance on Russian gas. Demand is falling after the region pumped a record volume of the fuel into underground storage to guard […]