Supply and demand.
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As more than half the nation has spent weeks in a deep freeze, the price of propane — used for everything from heating homes to powering farms — has skyrocketed, leading Washington lawmakers to question whether producers are manipulating the market.

The impact of record prices is particularly pronounced in rural states, where propane is more commonly used. In Colorado, residents saw prices nearly tripling in the past two weeks as freezing weather in the Midwest boosted demand on an already tight supply in the state. Since Jan. 16, prices have jumped to as much as $6 a gallon from $2.30.

In Iowa, Republican Sen. Chuck Grassley has asked the Federal Trade Commission for a review of the market to make sure there are no cases of blatant production manipulation, which in turn would cause prices to rise.