Ten years ago, when Bob Beal paid $7,500 for a parking space on Beacon Hill, some of his friends thought he was nuts.

But this year, two spots in the same garage changed hands for $135,000 each - and 10 more buyers put their names on a waiting list. So who's nuts now?"I'd say it looks like it was a pretty good investment," Beal said. "Wouldn't you?"

Of course, not all parking in this city is so expensive. A space in the garage under the Boston Common goes for $110 a month. All you have to do is sign up and wait your turn - which, at the present rate, would come in about seven years, according to the state agency that runs the 1,500-car garage.

On an average day, according to a recent study, 99 percent of the spaces in the financial district are filled by 10 a.m. By noon, the occupancy rate rises to 102 percent - the extra 2 percent reflecting illegally parked vehicles.

While many major cities have similar problems, Boston's is particularly acute, because the parking supply has been frozen since 1973, when the federal Environmental Protection Agency and a state environmental agency set a cap of 35,500 spaces in an effort to control smog.