NEW YORK (The Deal) -- Shares in Canada's Talisman Energy (TLM) rose almost 10% in after-hours trading Monday but retreated during the session on Tuesday as investors followed Carl Icahn into the restructuring gas producer. Shares were down 2.4% to $12.44 at 1:30 p.m. Tuesday.

The activist investor revealed late Monday that he controlled 5.97% of the group's equity and said he may seek talks with management. His Icahn Capital vehicle made the filing.

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

Icahn's position is worth about C$812 million ($786 million), though he acquired control of the shares for just $277 million, mainly by buying options to acquire shares rather than acquiring the shares directly. The 5.97% stake controlled by Icahn makes him Talisman's No. 2 shareholder, behind fund manager Franklin Resources Inc. and ahead of BlackRock Inc.

Calgary, Alberta-based Talisman reappointed former CEO Hal Kvisle in September last year to arrest a slumping share price, driven lower by poorly timed acquisitions and disappointing returns from its North American shale gas operations and its mature North Sea oil assets.

Kvisle promised to sell peripheral and nonperforming assets worth $2 billion to $3 billion and find partners for his company's North Sea business and sell down or exit Canadian gas fields. But the executive has since drawn criticism for the slow pace of sales.

Talisman opened a data room at the end of July, providing information on assets, including its 12% stake in the Ocensa pipeline in Colombia, the Norwegian portion of its North Sea assets and the Canadian Montney and Duvernay gas fields.

Talisman shares have fallen almost 50% from an early 2011 high of more than C$24. They closed Monday at C$13.15, up from C$11.77 five days ago, as rumors emerged that an unnamed investor had begun acquiring a significant stake in the business.

That still leaves a lot of room for improvement, according to some analysts. Talisman, which has a market capitalization of about C$13.6 billion, could be worth slightly over $27 billion if it succeeds in selling unwanted assets, cutting costs and improving performance at its North American and Asia Pacific operations, analysts at Sanford C. Berstein Research noted on Aug. 15.

Talisman welcomes "constructive input from shareholders," the company said, responding to Icahn's mooted plan to meet with management.

Icahn has a history of agitating for change at energy companies. He was instrumental in forcing Chesapeake Energy to change both its chairman and CEO, in 2012 and this year, respectively. His investment in Transocean Ltd., an offshore-rig contractor, preceded the exit of its chairman and the reinstatement of the company's dividend, though he failed to increase the payout to his desired level.

In September Icahn ended a months-long effort to block the buyout of computer maker Dell Inc. by founder Michael Dell. He has attempted to cajole Apple Inc. to commit more of its huge cash reserve to buying back shares, so far without success.

Shares in Talisman traded at $13.89 in the New York after-hours market on Tuesday morning, up $1.14, or just under 9%, on their U.S. close of $12.75 on Monday.

-- Written by Paul Whitfield in New York