WASHINGTON — Consumer prices rose less than expected in May, fresh evidence that the recession is keeping inflation in check.

The Labor Department reported this morning that the consumer price index rose a seasonally adjusted 0.1 percent last month, below analysts' expectations of a 0.3 percent rise.

Excluding volatile food and energy costs, core prices also increased 0.1 percent, matching expectations.

Low inflation enables the Federal Reserve to keep a key short-term interest rate near zero, where it has been for months.

The recession is holding down prices as the unemployment rate has reached a 25-year high and factories are operating at record-low levels. Workers concerned about their jobs are less likely to push for higher pay, while low consumer demand has made it difficult for companies to raise prices.

Gasoline prices rose 9.6 percent in May, before seasonal adjustment, the department said. But they are still much lower than last year, when prices at the pump topped $4 a gallon during the summer.

Due to that decline, consumer prices fell 1.3 percent in the 12 months ending in May, the steepest drop in 59 years. The core CPI has increased 1.8 percent since last year.