Natural gas prices were falling to four-week lows after the U.S. government reported a sharp buildup in the country's natural gas storage levels.
The price of natural gas fell 15 cents, or 3.4 percent, to $4.40 per thousand cubic feet, the lowest since late May.
The Energy Department said U.S. natural gas inventories rose by 110 billion cubic feet last week, much more than what investors expected. In the summer, natural gas is primarily used to fire on-demand power plants when there is a need for additional electricity, particularly on hot summer days.
Other energy commodities also fell. Oil lost 66 cents to $105.84 a barrel. Wholesale gasoline fell a penny to $3.09 a gallon.