TPG-Axon, which owns 6.5 percent of SandRidge's outstanding stock, sent its first letter on Nov. 8 calling for CEO Tom Ward and the company's board to be replaced.
Mount Kellet Capital Management LP, which owns 4.5 percent of SandRidge's stock, issued a similar call a week later.
The investment firm contends the stock should be trading about $20 a share.
SandRidge closed Friday at $5.85 a share, up 18 cents.
TPG-Axon blames poor management for SandRidge being undervalued, despite its significant asset base.
“SandRidge stock has declined almost 80 percent from its IPO (initial public offering) level in 2007, and is the single worst performing energy stock over that period in the Russell 1000 index,” Singh wrote.