Years of US congressional efforts to bring the vast over-the-counter energy derivatives markets under tighter regulation started to pay off yesterday when the country’s futures watchdog warned it was “nearing the outer limits” of its authority to oversee energy futures markets.

Walter Lukken, acting chairman of the Commodity Futures Trading Commission, told a senate hearing into alleged “excessive speculation” in energy derivatives last year by hedge fund Amaranth that it was “appropriate to have this open dialogue...about what other tools are needed to adequately oversee” the markets.