Several gas pipelines run through Ukraine to the rest of Europe
By Rupert Wingfield-Hayes
BBC News, Moscow
Winston Churchill once famously described Russia as "a riddle wrapped in a mystery inside an enigma". This week Russia has once again lived up to its difficult reputation.
As an outsider it's extremely easy to be desperately confused by the way this country behaves.
Is Russia's decision to cut gas supplies to Ukraine simply a commercial dispute?
Is it the Kremlin extracting political revenge for Ukraine's Orange Revolution?
Or is it an even more convoluted conspiracy involving powerful political figures in Moscow and Kiev?
Depending on who you talk to, it's all of the above.
Talk to the deputy chairman of Russia's state gas giant Gazprom, Alexander Medvedev, and he'll tell you it's purely a commercial dispute.
"The rest of Europe pays more than $400 for each thousand cubic metres of gas it gets from Russia."
Alexander Medevdev says Gazprom needs 'alternative transit routes'
He tells me: "We have offered Ukraine extremely favourable terms for gas deliveries in 2009, but they have still refused to sign a new contract.
"So now we have no legal basis to continue supplying gas to them."
All of this is true. Up to now Ukraine has got its gas at just $179 per thousand cubic metres. This year Russia wants to raise that to $250.
That's still far below what the rest of Europe pays.
But talk to Masha Lipmann, a well-known political commentator at the Carnegie Endowment for International Peace in Moscow, and you'll hear a very different story.
"Moscow can't pretend this is purely a commercial dispute" she says.
"There's little doubt that Russia is using its energy resources as a political tool."
But why? What does the Kremlin want to achieve?
According to those who subscribe to the political weapon theory, Russia's purpose is to bring down the government of Ukrainian President Victor Yushchenko.
The Kremlin has never forgiven Mr Yushchenko for leading the Orange Revolution in 2004, and for moving Ukraine out of the Russian fold and towards a much closer relationship with Europe and the US.
Mr Yushchenko has applied to join Nato, and says he wants Ukraine to eventually join the European Union.
This is anathema to many Russians who consider Ukraine a part of the Slavic heartland.
Prime Minister Vladimir Putin is famously supposed to have told US President George W Bush once that "Ukraine isn't even a state".
And then there are the conspiracy theories.
The first goes like this: Gazprom wants to build a pipeline down the Baltic Sea, bypassing Ukraine, to supply its gas directly to the rich markets of Western Europe.
But the project, known as "Nordstream" is hugely expensive, fraught with environmental problems, and unnecessary.
The current pipeline network through Ukraine is perfectly adequate. Except, that is, if Ukraine keeps jeopardising supplies to Europe.
Consider this from Gazprom's Alexander Medvedev on Friday: "The question is can we rely on a transit country like Ukraine? Obviously there is no positive answer to this question.
"This is why we believe it is necessary to develop, as soon as possible, alternative transit routes. We hope that Europe takes the necessary steps to support this."
Perhaps not so far-fetched then.
But the final theory is even more outlandish: that powerful political figures in Ukraine are colluding with the Kremlin to foment the crisis and bring down President Yushchenko.
That would allow his political enemies to gain power.
Who would benefit from such a scenario? Ukraine's increasingly powerful Prime Minister Yulia Timoshenko.
Supporters of this theory say we can expect Ms Timoshenko to turn up in Moscow some time next week, sign a deal with the Kremlin, and return home to Kiev in triumph, having saved Ukraine from disaster.