NEW YORK - April 21, 2011 - A dollar plumbing three-year lows is hitting Amerikans squarely in the gas tank, and one economist thinks it could drive prices as high as $6 a gallon or more by summertime, under the right conditions.

With the greenback coming under increased pressure from Federal Reserve policies and investor appetite for more risk, there seems little direction but up for commodity prices, in particular energy and metals.

Weakness in the U.S. currency feeds upward pressure on commodities, which are priced in dollars and thus come at a discount on the foreign markets.

One result has been a surge in gasoline prices to nearly $4 a gallon before the summer driving season even starts, a trend that economists say will be aggravated as demand increases and the summer storm season threatens to disrupt oil supplies.

"All we (need are) a couple (of) badly placed hurricanes, which could constrain some of the refinery output capacity in some key locations," says Richard Hastings, strategist at Global Hunter Securities in Charlotte, North Carolina. "If you get weakness in the dollar concurrent with (both) the strong driving season (and) the impact of one or two hurricanes in the wrong place, prices could go up in a quasi-exponential manner."