The Commodity Futures Trading Commission plans to issue a report next month suggesting speculators played a significant role in driving wild swings in oil prices -- a reversal of an earlier CFTC position that augurs intensifying scrutiny on investors.

In a contentious report last year, the main U.S. futures-market regulator pinned oil-price swings primarily on supply and demand. But that analysis was based on "deeply flawed data," Bart Chilton, one of four CFTC commissioners, said in an interview Monday.

The...