PENSACOLA, Fla. (AP) - The Panhandle's largest private landowner on Thursday sued a Houston-based company responsible for the drilling fluids including mud that should have controlled the pressure in the well and prevented the blowout of BP's failed Gulf of Mexico oil well.

Real estate developer St. Joe Co. is seeking unspecified damages against M-I SWACO for a decline in the value of its 577,000 Panhandle acres and in its developments. At its worst point during the massive Gulf oil spill, the company said it lost about $1.4 billion in stock value.

The company's stock closed at $24.13 a share on Thursday. It had reached a six-month high of $37.44 on April 29 before the spill began to reach the coast.

A month after the spill, an international airport opened in Panama City on land donated by St. Joe and surrounded by land the company planned to develop. St. Joe had courted Southwest Airlines to service the airport under a unique plan in which the company agreed to pay the airline's fuel bill if it did not reach passenger goals in the opening year.

St. Joe lead counsel William Brewer said the company had a positive future before the spill.

"Sitting in the chair that any one of the executives at St. Joe sits in, you would have said on April 19 that you were as proud as punch at what you had done and that our future was very bright indeed," he said.

But less than two months later, St. Joe had lost more than 40 percent of its stock value.

M-I SWACO did not return phone messages and e-mails seeking comment on the lawsuit filed in Superior Court in Delaware. St. Joe filed a similar action against Halliburton on Aug. 4 and the company has said it plans to sue others involved in the BP well.

On April 20, an oil rig owned by Transocean Ltd. and leased by BP exploded 50 miles off the Louisiana coast, killing 11 workers and triggering the world's worst peacetime spill. Oil fouled the beaches in Gulf coast states and drove away tourists.

The company being sued, M-I SWACO, is a joint venture between Nevada-based Schlumberger of and Smith International of Delaware.

According to the lawsuit, SWACO officials ignored safety warnings on the Deepwater Horizon.

"Eleven crewmembers lost their lives. ... Since that time, experts have universally concluded that the decision to remove drilling mud before the well had been finally plugged was a significant cause of the explosion," the lawsuit states.

"M-I SWACO deliberately chose to implement and execute a drilling fluid program on the Deepwater Horizon it knew was grossly negligent, unsafe and inherently flawed," the lawsuit says.

Messages left for the press contact at M-I SWACO weren't immediately returned Thursday.