We recently received a gas bill from our local utility, PSE&G, that was surprisingly high. That's because we weren't home when the professional meter reader was in our neighborhood, and the utility estimated our gas usage for that month. We got a bill for over $300 in estimated gas usage, when our normal amount might be closer to $50!
After a frantic phone call to the utility, we found out the estimate was based on the company's formula which is a follows: They take the highest reading for that particular month over that past three years and then apply a premium. (We weren't told what that premium is.)