Xcel Energy has temporarily stopped billing North Dakota ratepayers for natural gas they weren't charged for last winter because of a meter reading snafu, a state regulator said.

Susan Wefald, president of North Dakota's Public Service Commission, said Xcel Energy customers who have already gotten a delayed natural gas bill do not need to pay it for at least 60 days. The commission may decide to extend the grace period, Wefald said Wednesday.

Some Xcel customers may have a situation where part of their utility bill is due at the normal time, while payment of another portion may be delayed without any penalty. Customers who are not sure which is which should check with the utility, Wefald said.

"People are receiving really weird bills. Some people are getting two bills on the same day, with different amounts. There are mathematical errors on some of the bills," Wefald said. "The commission is really concerned about this, and also realizes what a hardship it is for people to receive these large natural gas bills in the middle of summer."

Xcel Energy supplies natural gas to about 44,000 customers in Fargo, West Fargo, Grand Forks and some smaller nearby communities.

Bonnie Lund, an Xcel spokeswoman, said about 4,400 customers were not billed for last winter's natural gas usage because some newly installed meter reading equipment did not work correctly. For residential customers, the amounts have ranged from $200 to $800 or more, she said.

The equipment allows Xcel to read natural gas meters remotely. The technology was first installed years ago, and the new gear was put in last fall because batteries on the existing equipment needed to be replaced, she said.

"It was more economical to replace the modules than to do the labor involved to change the batteries," Lund said.

She said the North Dakota meter reading problems were first discovered in February. It does not affect electric bills, she said.

Xcel has already estimated the customers' natural gas usage and billed them for it, but the utility is still discovering instances where the meter reading equipment malfunctioned, she said. The utility will delay sending the bills to those customers for an unspecified time.

Wefald said Xcel customers who have questions about their bills should call the utility to find out which portion of their bill does not have to be paid for at least 60 days. The commission also wants to hear customers' concerns, she said.

"We realize that none of this is the customer's fault. However, it is important that customers call Xcel Energy so that they don't get messed up on a portion of the bill that needs to be paid, while the commission is sorting through all the issues that are involved in this case," Wefald said.

Lund said Xcel, in estimating the natural gas bills for customers who had malfunctioning equipment, used a standard process that is employed when any customer's meter does not work.

Xcel compares the time during which the meter did not work to the same periods during the previous two years, then estimates the bill using the lower of the two figures, she said.

"This year in particular, that approach is beneficial to the customer," she said. "We have had a colder winter this year than it was during the previous two years."

Wefald said the commission sent a list of questions about the meter reading problems to Xcel Energy on July 2, but she said the utility has not responded. Lund said Xcel hoped to submit its response Thursday.