A natural-gas price slide in overnight electronic trading on the New York Mercantile Exchange triggered a 20-second automatic trading pause for the August Henry Hub natural gas futures contract, according to a spokeswoman for CME Group Inc., which owns the Nymex.

No trading orders were canceled during the pause, the Chicago-based spokeswoman, Laurie Bischel, said in a phone interview.

The August contract dropped as much as 5.6 percent, reaching an intraday low of $4.601 per million British thermal units at 7:42 p.m. yesterday in New York before reversing losses. The July and September contracts fell as much as 7 percent.

August gas fell almost 15 cents within one second, according to Bloomberg data. Volume in the August gas contract jumped above 200 at about 7:42 p.m. before tumbling, Bloomberg data show. Volume also rose in the July and September contracts.

Natural gas for July delivery fell 17.3 cents, or 3.6 percent, to settle at $4.674 per million Btu after dropping as low as $4.51. Gas for August delivery slipped 17 cents, or 3.5 percent, to $4.704.

Computer Programs

The overnight decline may have been caused by algorithmic trading, said Mike Fitzpatrick, a partner with the Kilduff Group, a New York-based energy advisory company, in an interview today. In algorithmic trading, computer programs are used to enter orders and determine the timing, price or other aspects of the trade.

“The natural gas market saw sharp price swings in overnight trade that the exchange is standing by as valid trades as of this writing, although we can expect a further review about the highly unusual ‘flash crash’ and reversal to new highs,” Tim Evans, an energy analyst with Citi Futures Perspective in New York, said in a note to clients today.

“It’s ugly price action that does not reflect well on the market’s reputation for fair trade,” Evans said.

Commodity Futures Trading Commission Chairman Gary Gensler has said the commission will miss a mid-July deadline to impose limits on speculation in raw materials including oil, gas, gold and wheat.