An index of consumer prices in the metropolitan area fell slightly in the 12 months through May on declines in the cost of energy.

The federal Bureau of Labor Statistics Thursday reported its consumer price index for the 31-county region that includes Long Island dropped 0.1 percent in May compared with a year ago.

It was the third year-over-year decline in the index in 2015. The 0.1 percent drop matched that of March and followed flat year-over-year prices in April.

Last month, gasoline prices were off 27 percent from May 2014. The cost of electricity fell 6.4 percent and natural gas was down 18.2 percent.

Other household costs rose in May, year over year.

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Grocery prices were up 1.3 percent.

The cost of residential rents rose 2.6 percent while health care and clothing increased 3 percent and 3.6 percent, respectively.