In recent years, oil giant BP PLC used a well design that has been called "risky" by Congressional investigators in more than one out of three of its deepwater wells in the Gulf of Mexico, significantly more often than most peers, a Wall Street Journal analysis of federal data shows.

The design was used on the well that exploded in the Gulf of Mexico on April 20, killing 11 workers and causing America's worst offshore oil spill. The only other major well design, which is more expensive, includes more safeguards against a...