The difference in the official and unofficial rate for Argentinian pesos is now so pronounced that at least one bitcoin exchange has acknowledged it. Localbitcoins.com has decided to publish a 'blue dollar' exchange rate for the currency.

The escrow-based decentralised bitcoin exchange service has produced a symbol for the blue dollar rate called XAR, and is using it to calculate bitcoin exchange rates.

The black market rate in Argentina is a result of rocketing inflation, and tension over a possible default. This has led Argentinians to hoard dollars, while the authorities have imposed strict controls on purchasing US dollars through official channels. This has led the blue rate to rise.

“People from Argentina are requesting us to add these blue market trades because the official rate is useless,” said Jeremias Kangas, founder of LocalBitcoins.com, who would not reveal where he sourced the blue rate data. “The official rate is useless for trading bitcoins or anything else, so we have decided to add this blue market rate.”

Late last month, the Argentine government approved legislation pardoning tax dodgers who invest their undeclared foreign currency holdings in the construction, oil and gas industries. The amnesty will allow the investors to buy dollar bonds.

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estimates the historical blue rate (i.e. USD black market) against the official dollar rate over the last two years.