(REUTERS) -- Producer prices fell in December as companies paid less for gasoline and vegetables, although higher prices for light motor trucks pushed a measure of underlying inflation higher.
The Labor Department said on Wednesday its seasonally adjusted index for prices received by farms, factories and refineries fell 0.1 percent.
Economists polled by Reuters had expected wholesale prices to increase 0.1 percent.
Excluding volatile food and energy, core producer prices rose 0.3 percent last month, the biggest rise since July. That was above economists' expectations for a 0.1 percent gain.
The data appears to send mixed messages about inflation pressures in the U.S. economy.
A drop in energy prices has encouraged Wall Street and the U.S. Federal Reserve to forecast inflation will cool in coming months.
Energy costs for businesses fell 0.8 percent last month, with gasoline down 2.3 percent. Food prices fell 0.8 percent.
At the same time, higher core prices - if eventually passed on to consumers by businesses - might make the U.S. central bank more cautious about taking additional steps to help the still-struggling U.S. economy.
That said, about 30 percent of the gain in core prices were due to an increase in prices for light motor trucks, the Labor Department said.
Prices in auto sector have been affected in recent months by floods in Thailand that last year disrupted supply chains. Prices for light trucks rose 0.9 percent last month, the biggest rise since July.