Oklahoma-based SandRidge Energy adopts 'poison pill' plan

“SandRidge has not merely failed to even remotely maximize the potential of its assets, but it has destroyed stockholder value,” Mount Keller wrote in a letter last week to SandRidge's board.

That letter followed less than a week after TPG-Axon Capital called for a new CEO at SandRidge and for the directors to consider selling the company. TPG-Axon controlled 6.2 percent of SandRidge shares as of last week.

“Although we are enthusiastic about the value potential in SandRidge, we have grown increasingly concerned about the ability of this management team, or of the board of directors, to protect shareholder interest,” TPG-Axon CEO Dinakar Singh wrote in a letter to the SandRidge directors.

Besides the comments from the two active investors, passive investor Fairfax Financial Holdings on Friday told regulators it has increased its stake in SandRidge to 10.4 percent.

SandRidge shares gained 28 cents, or 5.2 percent, Monday to close at $5.62 on the New York Stock Exchange. In after-hours trading, the stock price slipped 13 cents, or $2.3 percent, to $5.49.

CONTRIBUTING: Jay F. Marks and Paul Monies,

Business Writers