WARRENVILLE, Ill. — Due to commodity prices doubling in the past six months, Navistar International has decided to increase prices on International trucks, effective immediately.

The price increases, says the truckmaker, will vary by model, topping at $1,600 per truck.

The company explains that prices have soared for commodities essential to truck manufacturing, such as crude oil, steel, aluminum, copper, and precious metals used in new emissions-compliant diesel engines.

Since the beginning of 2008, steel has increased 100 percent, aluminum by 22 percent, platinum by 32 percent and copper by 23 percent. Crude oil prices have jumped by more than 40 percent, according to Navistar.

"We are acutely aware of the financial constraints that many truck customers are currently facing and have been working diligently to absorb as much of these costs as possible," said James L. Hebe, who was named senior vice president of Dealer Operations earlier this year. "However, global commodity spikes are affecting all manufacturing and we finally, regretfully, must now share those additional costs with the customer."

Navistar says it is working to mitigate the higher commodity prices, as well as offset the negative impact of a weakened U.S. dollar, by "attacking operational costs wherever possible and by negotiating greater efficiencies with suppliers."