The likelihood of a complete collapse is difficult to assess, in part, engineers and legislators say, because BP hasn’t shared enough information to evaluate the situation. But a handful of clues suggest that the company is concerned. On Friday, BP spokesperson Toby Odone acknowledged that the 45-ton stack of the blowout preventer was tilting noticeably, but said the company could not attribute it to down-hole leaks. “We don’t know anything about the underground portion of the well,” he said. But, the stack “is tilting and has been tilting since the rig went down. We believe that it was caused by the collapse of the riser.” The company is monitoring the degree of leaning but has not announced any plans to run additional supports to the structure.

As many have speculated, and as the New Orleans Times Picayune reported Friday, concerns over structural integrity are what led BP to halt “top kill” efforts late last month. When it was digging this particular well, the company ran out of casing–the pipe that engineers send down the hole–and switched to a less durable material called liner. This may have created several weak spots along the well that would be particularly vulnerable to excessive pressure or erosion. So instead of sealing the well, the company has been focused on trying to capture the oil as it flows out the top.

The symptoms are well-documented: The Exxon Valdez oil spill in 1989 touched off a wave of suicides, domestic violence, bankruptcies and alcoholism in Alaska that created an entire literature on the unique and confounding psychology of technological disaster.