Activist investor Fir Tree Partners on Nov. 20 opposed SandRidge Energy Inc.'s (NYSE: SD) $746-million deal to buy rival Bonanza Creek Energy Inc. (NYSE: BCEI), saying an acquisition would drain all of the oil and gas producer's cash.

"We believe this proposed acquisition represents a complete about-face by [SandRidge's] management on its post-bankruptcy strategy," Fir Tree Partners, which owns about 8.3% of SandRidge, said in a statement.

SandRidge emerged from bankruptcy late last year, while Bonanza did so in April following a recovery in oil prices after a two-year slump.

As of Sept. 30, Oklahoma-based SandRidge's cash and cash equivalents stood at $133.2 million.

Shares of SandRidge, which had fallen nearly 22% since the beginning of the year, dropped another 15% on Nov. 15 after the deal was announced.

Bonanza Creek's shares closed at $32.07 on Nov. 15, well below SandRidge's offer price of $36 per share, suggesting investors were skeptical the deal would close.

Fir Tree also said SandRidge was paying an "unjustified premium" for Bonanza Creek.