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 natural-gas blowout of the kind that destroyed the Deepwater Horizon.

A Journal analysis of records provided by the U.S. Minerals Management Service shows that BP used the less costly design—called "long string"—on 35% of its deepwater wells since July 2003, the earliest date the well-design data were available. Anadarko Petroleum Corp. , a minority partner of BP's in the destroyed well, used it on 42% of its deepwater Gulf wells, though it says it doesn't do so in wells of the type drilled by BP.

Both companies used the design much more often, on average, than other major Gulf drillers. Out of 218 deepwater wells in the Gulf drilled since July 2003, 26% used the long-string design. It derives its name from its use of a single, long "string" of pipe from the sea floor to the bottom of the well.