Information provided by Theflyonthewall.com

The Treasury Department offered a further $18 billion of its holdings in AIG (AIG) common stock, which is expected to lower the government's ownership stake in the company below the 50% level. In connection with the offering, AIG plans to buy up to $5 billion in shares at the initial public offering price.

Plains Exploration (PXP) agreed to acquire certain BP (BP) Gulf of Mexico interests for $5.55 billion and also agreed to purchase Shell's (RDS.A) stake in one of the related Gulf fields for $560 million.

Among the notable gainers Monday were GT Advanced Technologies (GTAT), up 12% following a positive mention from Piper Jaffray in a note to investors, and Peregrine Pharmaceuticals (PPHM), up 4% after two firms raised their price targets on its shares and the company's quarterly revenues beat consensus.

Among the noteworthy losers were Geron (GERN), down 57% after the company said it was discontinuing a trial of an experimental cancer drug, and Nordion (NDZ), down 35% after it was unsuccessful in its claim for specific performance or monetary damages in a case against Atomic Energy of Canada Limited.