At 07.00am (AEDT), the dollar was trading at $US0.7021/29, up from Wednesday's close of $US0.6919/24.
During offshore trading, the local unit moved between a low of $US0.6860 and a high of $US0.7112.
Local foreign exchange markets closed at 5.00pm AEDT on Wednesday for New Year's Eve.
CommSec chief equities economist Craig James said the dollar pushed higher in line with a sharp rise in commodities prices during offshore trading.
"There were some huge gains in terms of nickel, gold, oil and the other base metals so certainly there may have been a sympathy rally for the Aussie dollar on the back of that,'' Mr James said.
Crude oil for February delivery was up $US5.57 to settle at $US44.60 a barrel on the New York Mercantile Exchange, its highest level since December 12.
The price of gold was also higher: the price of gold futures for February delivery was up $US14.30 to $US884.30 an ounce.
A positive day on US equities also encouraged risk appetite for the high-yielding Australian dollar.
The Dow Jones Industrial Average gained 1.25 per cent, the S&P500 index was up 1.42 per cent and at the close of the New York session the NASDAQ had risen 1.7 per cent.
"We did have the equity markets up at the end of the year (and) that suggests a degree of optimism,'' Mr James said.
He cautioned against reading into the moves during offshore trading, however, given the thin trading conditions and lack of liquidity.
"We have to wait and see how things settle down in the early days of 2009 before we can get too carried away.''
Mr James expects the dollar to trade quietly during Asian trading, with direction to come from how commodities prices performed.
"If they hold on to the gains that they recorded on Wednesday, then the Aussie dollar may indeed have found a new base above 70 US cents,'' Mr James.
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