The producer price index for finished goods rose for the fourth consecutive month in October, mainly pushed by gas price hikes, the U.S. Labor Department said in a report.

The PPI rose 0.4 percent in October, following a similar increase in the past two months.

However, the rise was much less than economists' forecast of 0.8 percent as polled by Reuters.

Excluding foods and energy, the index fell 0.6 percent for the first time this year, mainly due to lower prices for light motor trucks and cars.

October's US producer price figures are badly distorted by the new quality adjustments applied by the statisticians to the price of cars and light trucks, Paul Ashworth, an economist at Capital Economics, said in a note.

The price increase for 2010 models were smaller than seen in past years, he added.

Prices for finished energy goods rose for 3.7 percent for the third straight month. Finished consumer food prices also fell 0.1 percent, surprising economists.

But the sharp rise in agricultural commodity prices is making itself felt at the earlier stages of production, with raw foodstuffs prices jumping in 4.2 percent month-on-month and intermediate food prices increasing by 1.3 percent month-on-month, Ashworth added.

He expects the recent jump in commodity prices to have a knock-on effect on both PPI and consumer price index inflation over the next few months.