An oil-drilling procedure called cementing is coming under scrutiny as a possible cause of the explosion on the Deepwater Horizon rig in the Gulf of Mexico that has led to one of the biggest oil spills in U.S. history, drilling experts said Thursday.

The process is supposed to prevent oil and natural gas from escaping by filling gaps between the outside of the well pipe and the inside of the hole bored into the ocean floor. Cement, pumped down the well from the drilling rig, is also used to plug wells after they have been...