The survey showed a 28 per cent gain in the fourth quarter alone to US$7.3 billion, IDC said.

IDC also found that Google's net US market share declined for the first time in two years due to slower growth in domestic fourth-quarter sales.

The market leader's net US Internet advertising market share was down 0.5 per centage points to 23.7 per cent last quarter.

Google's estimated net US Internet advertising sales excluding the cost of payments to partners in their networks grew by a little more than 40 per cent in the fourth quarter, but its year-on-year growth rate in the quarter before had been 50 per cent, IDC said.

'If a merger between Microsoft's new media business and Yahoo would come to pass, the combined entity would have a net US advertising market share of about 17 per cent based on our fourth-quarter data,' says Karsten Weide, program director for IDC.

'It would not quite bring Microsoft-Yahoo to where Google is in online advertising in the US, but it would give them a much better fighting chance than if they went it alone.' -- AFP