SOUTHFIELD (Michigan) • When a woman CEO steps down, there is usually a man waiting to fill her shoes.

Of at least 24 female chief executive officers of S&P 500 companies who have stepped down since 2009, all but three have been replaced by men, according to an analysis of data on executive departures compiled quarterly by recruiter Spencer Stuart.

That includes PepsiCo CEO Indra Nooyi, who announced on Monday that she will leave the post in October, and at least four other women this year.

The largest companies have struggled to elevate women, who hold only about 5 per cent of CEO positions. Progress has stalled even amid the revelations of harassment or other misconduct brought to light by the #MeToo movement and pressure from investors such as State Street Corp and BlackRock to get boards to add diversity.

"Despite the advances that females have made over the last 10 years, and the big push that's going on to get them into executive positions, if you look at the talent pool of available individuals, it's going to be mostly men," said Mr Tom Flannery, who leads the global chief executive board services practice at Boyden, an executive recruiter.

After Ms Nooyi's departure, there will be just 23 female CEOs leading Fortune 500 companies, making up less than 5 per cent of all CEOs at these companies, down from 32 female CEOs last year.

There has been a spate of resignations of female CEOs over the last year, MarketWatch noted.

In May, Ms Denise Morrison stepped down as CEO of Campbell Soup and, in April, Ms Margo Georgiadis resigned as CEO of toymaker Mattel. Last year, Ms Meg Whitman quit as CEO of Hewlett-Packard, and Ms Irene Rosenfeld stepped down as CEO of food and beverage company Mondelez.

Among the high-profile women who remain at the helm of Fortune 500 companies: Ms Mary Barra, CEO of General Motors, Mrs Ginni Rometty, CEO of IBM, Ms Safra Catz, co-CEO of Oracle, and Ms Michele Buck, CEO of The Hershey Co.

Ms Nooyi, 62, who will stay on as chairman until early next year, is being replaced as CEO by Mr Ramon Laguarta, 54, who has been a candidate to take over since a promotion last year to president.

In addition to being PepsiCo's first woman leader, Ms Nooyi, who is from India, is also the first foreign-born CEO of the company, whose revenue topped US$63 billion (S$86 billion) last year.

In the executive ranks, women tend to concentrate in positions such as chief financial officer, general counsel and head of human resources.

Those roles are less likely to result in promotion to CEO than executives who serve as president or chief operating officer, jobs most often held by men, especially when there is a female at the helm.

Kohl's Corp is a rare exception because both its CEO, Ms Michelle Gass, and its president, Ms Sona Chawla, are women.

The blame falls partly to corporate boards, which are "overbalanced by males", said Mr Flannery. "Not only are they dominated by males, but the males that are on boards are mostly baby boomers, some are even war babies, and there are very few Gen Xers and even fewer millennials," he added. "These are people to whom the whole female gender movement is new."

Ms Debra Crew's promotion to succeed Ms Susan Cameron as CEO at Reynolds American early last year was the first female-to-female handover in the S&P 500 in six years, according to Spencer Stuart data.

The distinction was short-lived because even before she took the job, British American Tobacco said it would buy Reynolds. Ms Crew departed the company late last year.

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