What is the dispute about?
Prices and politics. Ukraine says it cannot afford to pay the $450 per 1,000 cubic metres of gas demanded by Gazprom. Russia claims it is only asking for $250 per 1,000 cubic metres, compared with $195 in 2008. Gazprom alleges that Naftogaz, Ukraine's state energy firm, still owes it $600m for 2008; the Ukrainians dispute this.
Which countries are affected?
Gazprom has now stopped gas supplies to Europe via Ukraine, accusing Kiev of shutting down all four pipelines and siphoning off gas for itself. The impact has been felt most acutely in Bulgaria, Romania, Greece, Macedonia, Croatia, Serbia, Bosnia and Turkey, although it is now affecting France, Germany, Italy, Austria, Poland, Hungary and the Czech republic. Britain, which imports only 3% of its gas from Russia, compared with the EU's 25% average, is unaffected.
Are people beginning to suffer?
With sub-zero temperatures continuing throughout mainland Europe, tens of thousands of people, mainly in eastern Europe, have no heating in their homes. Countries are urging citizens to switch to alternative fuels and are trying to import gas and other fuels by other routes. Ukraine has enough gas in storage until the spring.
Are there alternative routes?
Yes. Gazprom, which shipped 300-350m cubic metres a day to Europe via Ukraine, claims it is now providing 150m cubic metres via the Yamal pipeline to Europe and about 50m cubic metres via the Blue Stream pipeline to Turkey.