The heating bill this month brings householders a chilling reminder of how much natural gas prices have gone up this reason. Mark Reinders with MidAmerican Energy says it’s largely a matter of supply and demand. He says there’s been some volatility in the price in recent weeks, with the cost of natural gas going up in recent days even more than analysts had predicted. Reinders says in many cases the use of natural gas in the northeastern states directs whether prices in our part of the nation go up or down…and the demand is up. From the company’s offices in Sioux City, Reinders says they spent last summer stockpiling natural gas purchased at lower prices. He says before the end of October, MidAmerican had about 70-percent of customers’ estimated needs for the whole winter already purchased and stored. Reinders says having the fuel purchased ahead of time helps the utility control prices as much as possible. He says they can withdraw from the storage when there’s day-to-day demand and don’t have to buy it on the higher-priced spot market. Analysts had warned us as long ago as early summer that the price of natural gas would go up a lot this winter, though more recent market reports say though prices are indeed soaring, the supply is about where it was a year ago or even slightly higher, which should push prices downward. MidAmerican supplies natural gas to customers in much of Iowa, Nebraska and southeastern South Dakota.