Canadian oil company Talisman Energy Inc. (USA) (NYSE: TLM) is flirting with its 52-week high on heavy volume today on the strength of a tweet by hedge fund activist Carl Icahn. According to a filing with the SEC, the corporate raider bought 61,554,602 shares, which translates into a 5.97 percent stake of TLM for $277 million. The billionaire investor is now sitting on 61 million shares of the company. In the 13D document, Icahn cited undervaluation, asset sales, restructuring, and Board representation as potential outcomes of his activist stake in Talisman. On an interesting note, as of the end of the last quarter, a close associate of Icahn’s, Keith Meister, was TLM’s largest shareholder with a $103.5 million position in the company. This is roughly one-sixth the size of Mr. Icahn’s new stake.

Disclosed approx 61 million share position in Talisman Energy. May have conversations with mgmt re strategic alternatives, board seats, etc.

— Carl Icahn (@Carl_C_Icahn) October 7, 2013

Talisman Energy is an oil and gas producer which operates in the North Sea, Southeast Asia, North America, and the Middle East. The company has a current market cap of $13.34 billion, and although shares gapped sharply higher earlier this morning, they are currently trading down 1.73 percent on unusually heavy volume.

Aside from Icahn’s recent move on Talisman, other large hedge funds have made substantial trades over the past week:

1. Ricky Sandler and Eminence Capital upped their Aeropostale (NYSE: ARO) position. The stake represents 5.4 percent of the company and is valued at $39.2 million.
2. William Ackman reduced his Herbalife (NYSE: HLF) short, replacing it with long-term puts.
3. Richard Perry cut his shares in J.C. Penney (NYSE: JCP) by 9 million.
4. Daniel Loeb upped his position in Sotheby’s (NYSE: BID) to a 9.3 percent stake in the company.
5. Stephen Mandel filed a 13G with the SEC on 3 October announcing a 5.3 percent stake in Pandora Media Inc. (NYSE: P).
6. Jeff Ubben and ValueAct now own 9.7 percent of Rockwell Collins (NYSE: COL).

It will be interesting to see how Icahn plans to leverage his new position with talisman energy. He is not known for his gentle handling of CEOs in his quest for dramatic change within a company. Oil and gas company shares are up collectively by approximately 12.5 percent thus far this year, but Talisman shares have remained essentially flat failing to gain substantial traction for any length of time. One can only think that Icahn sees something in the company and feels he can fix what ails it. He probably will.

Disclosure: The author has no position in the stocks mentioned in this article, and does not intend to initiate any position in the next 48 hours.