U.S. consumer prices flat on cheaper energy

Analysts polled by Reuters were expecting the Consumer Price Index to rise 0.1 percent after a 0.1 percent slide in August.

So-called core prices, which exclude volatile food and energy costs, were also milder than expected, gaining 0.1 percent in the month instead of the 0.2 percent consensus forecast. Federal Reserve officials watch core prices carefully as a sign of future trends in inflation pressures.

Energy costs declined 1.9 percent in September after a 3.1 percent drop the previous month. Energy services prices, which include costs for natural gas and electricity, tumbled by 3.2 percent, the biggest decline in the 61-year history of the data series.

Gasoline prices fell by 0.6 percent after a 4.2 percent fall in August.