It's quite possible that Philadelphia has entered the era of the She-E-O.

When Campbell Soup Co. tapped Denise M. Morrison Tuesday to be its chief operating officer and likely next chief executive officer, it meant that three of the 10 biggest and best-known public companies based in the region will be headed by women as of next summer.

The others are Sunoco Inc., which hired Lynn Laverty Elsenhans as CEO in July 2008, and DuPont Co., which promoted Ellen Kullman to CEO in September 2008.

Combined, the three executives are entrusted with about $57 billion of shareholder value - greater than the market capitalization of Comcast Corp., the most valuable local company at $50 billion.

Some analysts were disappointed that the Camden food-maker hadn't gone outside its ranks for a successor to Douglas R. Conant, who has been CEO since 2001. Morrison has been president of the company's North America soup, sauces, and beverages unit for the last three years.

Investors react to all sorts of uncertainty, including news of a change at the top. Indeed, Campbell Soup shares fell 70 cents, or 1.9 percent, in the first two days after word of the management changes broke. They gained back 34 cents Friday to close at $36.09.

That share-price decline tracks the findings of research by a professor at the University of Virginia, who found a definite gender effect on stock prices when companies pick a woman as its CEO.

Erika H. James and coauthor Peggy M. Lee, of Arizona State University, analyzed 1,624 announcements involving the hiring of top management, including CEOs, chief financial officers, chief operating officers, presidents, and executive vice presidents, from 1990 through 2000.

In their paper, published in Strategic Management Journal in 2007, they wrote that the naming of a female CEO resulted in a more negative immediate market reaction than the announcement of a male CEO. James called the decline, calculated over three trading sessions, "statistically significant."

They found a decline in share price of 2.5 percent for female CEO appointments compared with a drop of 0.5 percent for men.

"We attribute the findings to an increased perception of risk for women CEOs because there are fewer historical examples of women in this position," James wrote in an e-mail.

Tara Weiner, managing partner for the Greater Philadelphia region for Deloitte L.L.P., said there were more managerial opportunities locally for women than in years past.

"The reality is that it takes a lot of focus and persistence over a long period of time to change the status quo," she wrote in an e-mail. "While there have been modest gains in women becoming C-level executives and board members in recent years, the trends are, in fact, changing for the better."

Of the 529 CEO appointments that James reviewed from the 1990s, only 17 were filled by women, or "She-E-Os" as she called them in the title of the paper.

That's truly abysmal for a nation where women are 47 percent of the total U.S. workforce and 40 percent of the managerial ranks, according to a recent report by the Government Accountability Office.

Even a column such as this one may serve to reinforce the perceptual bias of the CEO as nearly always male. In their research, James and Lee looked at how the press reported on the hiring of female CEOs and found that such articles call attention to their gender and include "extraneous" information on their family.

I'll do my best to avoid the extraneous, but I do think the naming of female CEOs at Sunoco, DuPont, and soon at Campbell Soup should be seen as significant because these companies are household names nationally.

They aren't the only local examples of powerful female leaders. Women run some of Philadelphia's biggest institutions. Amy Gutmann has been president of Philadelphia's biggest employer, the University of Pennsylvania, since 2004, having succeeded a decade of Judith Rodin. Ann Weaver Hart has been in charge of Temple University since 2006.

Women entrepreneurs have started their own companies and grown them into sizable, locally based enterprises, such as Rebecca Matthias, who'd started what is now Destination Maternity Corp., and Carol Ammon, cofounder of Endo Pharmaceuticals Holdings Inc.

Let's take nothing away from them, but face it: Everyone looks at the Fortune 500 list of the biggest U.S. companies each year and wonders why only 13 women sit in the big chair.

Is the glass ceiling so much more unbreakable at the biggest of the big?

The Philadelphia region isn't home to many big Fortune 500 companies. Only 14 companies with headquarters here appeared on the most recent list. That makes it all the more remarkable that Philadelphia could claim the greatest concentration of women CEOs among the Fortune 500 in mid-2011.

Like the career of an NFL running back, the average tenure of a CEO is four years. Elsenhans and Kullman are each two years into their tours of duty, which happened to coincide with a deep recession and stock market correction.

Maybe it's not fair to look at the stock prices to judge their progress - DuPont's stock price is 1.9 percent lower than it was before Kullman took over, and Sunoco shares are up 5.2 percent since Elsenhans came aboard.

But then again, I'd report that if they were men, so isn't that a small step toward gender balance?