Building materials group CRH surged up nearly 4% to €37.73 in London and closed up 2.1%, or 80 cent, at €37.29 in Dublin - its highest ever closing price - on talk of a possible break-up of the company.
London based traders said a report looking into the break up value of the company had renewed market speculation.
A Dublin based trader said that there is current speculation that CRH could be a take-over target for a private equity group, but that a similar trend occured last week with UK plumbing and building materials group Wolseley.
He said that CRH is such a well managed company and there has always been the argument that if it was broken up into parts it would realise its value.
Overall the ISEQ closed up 4.5%, or €1.00, at €23.00 with ICG closing up 4.5%, or €1 at €23.00 after it emerged that management at the ferry operator are in a position to match a rival bid for the group.
Takeover vehicle Aella, which is owned and controlled by senior managers, said that ICG Chief Executive Eamonn Rothwell had bought 1,750,200 shares, which equates to 7.4% of the group, for €22 each.
That share price matches last week's €561m agreed offer by the Moonduster consortium of One Fifty One Capital and Irish shipping company Doyle Group.
The FTSE100 in London closed flat at 6,649, underperforming other European markets, as interest-rate worries dampened sentiment and retailers including Morrison and Tesco fell.
Tullow Oil closed up 57.5p to 504.5p after a positive analyst note from Merrill Lynch with a 560p target price.
Elsewhere, European shares closed higher on merger and acquisition talk surrounding insurers and banks.
Germany's DAX index hit a record close at 8,090 points, up 56.97 or 0.71% and in Paris the CAC-40 closed at 6,093 points, up 21.62 or 0.36%.
As Europe closed, Wall street was slightly higher as oil prices fell with the Dow Jones up 11 points, or 0.09 percent, at 13,647 and the Nasdaq was unchanged at 2,627.
In the New York crude market, oil fell more than $1 a barrel after a US. government report showed larger-than-expected increases in crude and gasoline stocks. U.S. crude was down $1.40 at $67.70.
Earlier in Tokyo, the Nikkei climbed 0.26% as stocks with exposure to European markets rose with the yen near an all-time low against the euro. The Nikkei share average added 48 points to 18,211.
