Around the Midwest, propane prices are rising and have tripled in cost to more than $5 per gallon during the last week. There are also fears there won’t be enough propane, which is used to heat homes and dry crops, among other things. The Energy Department said last week that supplies of propane had fallen to the lowest level on record for the second week of January.

“Missourians are justifiably concerned about the dramatic increase in propane prices, affecting their ability to heat their homes and care for Missouri-based livestock,” Koster said in a written statement.

The Missouri Propane Gas Association said the rising costs are caused by higher exports and increased domestic demand due to colder weather and large crop yields. It said more propane production due to improved fracking technology caused companies to seek more overseas buyers, leaving less available domestically during times of increased usage.

Sen. Mike Parson, R-Bolivar, called on Koster to investigate last week and said companies caused the shortage to boost profits.

“People in this state cannot afford that,” Parson said. “I believe this has all been inflated by the companies themselves to make millions and millions of dollars because they choose to export.”

Parson introduced a nonbinding resolution in the Senate on Monday asking the Justice Department to also investigate prices. A group of Republican senators representing rural areas of the state also said they would work to find suppliers with excess propane to see if they could redistribute some to areas that are running low.

House Speaker Tim Jones, R-Eureka, said the Missouri House would also look into the issue, but wasn’t sure which direction it would take.

Koster said consumer investigators in his office have already participated in a multistate conference call with propane industry leaders and will coordinate with officials in nine other Midwestern states to determine the cause of the price increase.

Last week, the U.S. Department of Transportation issued emergency declarations, allowing propane tank operators to cross state lines and drive for longer hours through the South, Midwest, New England and the central Atlantic states.

According to the Energy Department, 5.5 million U.S. households heat with propane, mostly in the Midwest and South.