Wall Street and Madison Avenue were equally bemused at Tuesday's surge in trading of shares in Interpublic Group - the globe's second largest agency holding company. Who? and why? were the words hanging on the lips of analysts and adfolk alike.

In the absence of answers to those questions, Wall Street's best guess was that Interpublic stock is undervalued in comparison with its rivals and that the market is taking advantage of a bargain buy.

Fred Searby, an analyst at J P Morgan confessed himself otherwise unable to explain why more than 7.9 million shares changed hands - over three times the group's average daily trading volume of 2.4m.

Of course, there could be a third reason curiously ignored by the wizards of Wall Street. Someone is quietly building a stake having read runes indecipherable to less psychic beings - or maybe a concert party is tuning-up for a bid.

Whichever, IPG's share price closed 7.5 percent up on the day at $15.34 (€13.17; £9.19) while the shares of peer companies Omnicom Group and WPP Group rose by less than one per cent - and at considerably lower volumes.

The increased trading trend was maintained through Wednesday with over 6.1 million IPG shares changing hands by the close of business at the NYSE. Share price, however, dipped by 3% to close at $14.88 (€12.79; £8.90).

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Data sourced from: AdWeek.com; additional content by WARC staff