HOUSTON - Although no cause has been determined, oil services contractor Halliburton Inc. says it finished a cementing operation 20 hours before a Gulf of Mexico rig went up in flames.

Halliburton is named as a defendant in most of the more than two dozen lawsuits filed by Gulf Coast people and businesses claiming the oil spill could ruin them financially.

In one lawsuit, two Louisiana shrimpers claim cementing contributed to the explosion. Halliburton said Friday it had four workers stationed on the rig, performing several tasks, including cementing -- a process of applying cement and water to a pipe used to prevent the wall of the hole from caving in during drilling.

According to a 2007 study by Minerals Management Service, cementing was a factor 18 of 39 rig blowouts in the gulf between 1992 and 2006.