In our (cold climate) area, it is pretty standard for buyers to ask for a year's worth of utility costs.
Sellers often provide a list (rather than the actual bills).
If using a realtor, ask what the standard approach is - I have seen buyers ask for utility costs before making an offer in some cases.
Also, if I call our local utility as a prospective buyer of the property, they will give me an average monthly cost based on last 12 months' usage (and they will tell you if it looks like the building was occupied based on usage - IF you ask). The utility reps used to look at the actual billing history month by month (and would look back more than 12 months to find usage if that was helpful), but have gotten a bit more limited/officious lately.