With an 18-month feasibility study in hand, Mayor Nutter has good reason to take the next step in exploring whether the city can get the right price and the right terms in a sale of the Philadelphia Gas Works.

The prospect of netting more than $300 million under the best-case scenario outlined by the city's financial advisers represents a brass ring that Nutter should try to grab.

While that goal may appear to be within the city's reach, however, the mayor also needs to watch out so he doesn't miss the mark - and come toppling off the carousel.

It's as likely that the terms of any deal to privatize the nation's largest municipally owned gas utility would fall well short of the predictions outlined last week in a study by Lazard Freres & Co. L.L.C.

Lazard's experts pegged PGW's liabilities at about $1.5 billion. So the bids for the company that provides gas service to more than 500,000 customers would have to come in well above that to be at all worth entertaining.

While city Budget Director Rebecca Rhynhart says the price could range up to $1.85 billion, she acknowledges that it might be as low as $1.5 billion - in effect, a wash, with no significant profit for the city treasury.

Under such a sale, the city would forgo its $18 million annual dividend payment from the utility, and Lazard said there's no assurance that tax revenues from a privatized utility would match the city's annual fee.

It may be that a potential profit of several hundred million dollars could be put to good use for such things as plugging the gaping hole in the city's pension fund. However, the city must weigh whether that immediate gain is worth sacrificing long-term revenue.

Beyond such bottom-line considerations, the Nutter administration also would have to see that PGW customers came out ahead. That means they should expect continued safe, reliable, and affordable service, at a minimum.

Sale proponents - among them, key members of the Pennsylvania Public Utility Commission - say that, in private hands, PGW would be able to speed replacement of the city's aging cast-iron pipelines. A rare fatal gas explosion last year that killed a PGW crewman raised the stakes in that effort. At this point, though, it is not clear how a private firm would be any better positioned financially to accelerate very expensive pipeline repairs.

In the short term, it's good news that state lawmakers and Gov. Corbett have authorized surcharges so that PGW itself can raise funds needed to expand maintenance work and make the system safer.

Whether a private owner would slim a PGW workforce already streamlined by nearly half under the much-improved management of the utility over the last decade is less of a public-policy concern, provided downsizing doesn't compromise safety. Certainly, though, the mayor must guard against crippling the utility through any exodus of PGW staffers like the several hundred retirement-eligible line managers, who could get pension jitters merely due to talk of a sale.

The mayor says he'll only sell PGW at a profit, and that "no judgments or decisions have been made." Those are welcome assurances. Nutter must be willing to take down the For Sale sign if a PGW deal doesn't make sense.