The list includes marquee names such as Mary Barra of General Motors (GM) at No. 1 and Mattel (MAT) CEO Margo Georgiadis at No. 49. Twenty-six members of this elite group hold the CEO title, a rare feat in the world of business. (Women run only about 6% of Fortune 500 companies.)

So what does it take for a woman to ascend to the top of the corporate ladder? A forthcoming study by the recruiting firm Korn Ferry, in partnership with the Rockefeller Foundation, identifies several key factors.

In interviews with 57 female CEOs of Fortune 1000 companies—38 who currently hold the title, 19 who did recently—one particular commonality stood out: 65% of the women surveyed said they’d never thought about being a CEO until someone else told them they had that potential. And just 9% of the women said they’d always wanted to be CEO.

Those findings may come as a surprise to those who assume CEOs pursued that goal. But they also highlight one way women could break open the playing field and better compete for the top job at the world’s biggest companies.

Jane Stevenson, global leader for CEO succession at Korn Ferry, says she now asks other female executive clients—non-CEOs who might one day ascend up the ranks—one simple question: “Are you comfortable owning the power yourself, or do you need to support someone else’s power to have the most impact and to feel the most fulfilled?”

That question, which many of the women acknowledge they had never thought about before, could have real benefits for breaking the glass ceiling, Stevenson says. “To look at it as an actual indicator of potential CEO capability, instead of sticking to your knitting—it could create some very different outcomes for women,” she says. For example, one relatively young Fortune Most Powerful Women alum—Stevenson declined to name her—was thinking about retiring to serve on boards of directors. Stevenson’s question inspired her to stay in the game and try to land a CEO job “as opposed to calling it 10 years early,” Stevenson says.

The study also notes that women shouldn’t count themselves out for a CEO role just because they didn’t start out on that track. Of the four types of paths the 57 women (23 of whom work for Fortune 500 companies) took to the corner office, the least common route was the one where people knew early on—in college or shortly thereafter—that they wanted to get their MBA and move up the corporate ladder. Most female CEOs took less predictable paths to power.

Are you a woman who might want to be CEO some day? Here are some tips from the study that could help you keep that door open.

1. Skip Liberal Arts and Study STEM

Of the 57 female CEOs interviewed, 40% of them had college degrees in science, engineering, or math. That was double the share that studied either arts and humanities or economics and finance.

The STEM background helped the women prove they could hack it in a male-dominated field and “also had the added benefit of leading them into careers or jobs where results were very measurable, in black and white,” says Evelyn Orr, vice president and COO of Korn Ferry’s research institute. Objective metrics helped reduce the potential for gender bias to work against the CEOs, she adds: “The women self-reported: ‘They couldn’t not promote me—I had dollar signs next to my name!'”

GM CEO Mary Barra, for one, studied electrical engineering, and tells Fortune that the best advice she ever got came from her parents, “who encouraged me to work hard and pursue my early love of math.” Leanne Caret, the CEO of the Defense, Space, and Security division at Boeing (BA) and No. 30 on this year’s MPW list, also says that her high school sport of choice was math club.

2. Seek P&L Experience

While the ranks of women in the C-suite have swelled, the proportion of female CEOs at Fortune 500 companies has been relatively flat for years. So where’s the disconnect? According to the researchers behind the study, a differentiating factor is whether or not a female executive has experience owning a profit and loss statement.

Managing a budget or running a P&L is something women haven’t historically had access or encouragement to do. Yet for women who run Fortune 1000 companies, “the seminal experience that was pivotal across those was P&L leadership,” Stevenson says.

So when the opportunity arises, a woman should seize it—or at minimum look for roles where she can get hands-on with the financial side of the business. It’s more important than seniority or even face time with a company’s current CEO, Stevenson says. Running a P&L “is going to really be imperative to be considered as a CEO,” she says. “Don’t walk, run, for P&L experience.”

3. Shake Off Sexism

Another common trait of female CEOs: resilience. While many survey respondents noted that they had experienced sexism in their career, they all had strategies for overcoming it—whether by staying positive and upping their dedication in the face of detractors or by ignoring it and moving on. “They just didn’t get as hung up on that,” Orr says.

One CEO recalled a previous job in which she’d told her manager she hoped to make partner within five to 10 years, only to be told to erase it from her evaluation because it was “irresponsible” to have such an unrealistic goal on file with the human resources department. The woman began looking for a new job the next day.

Aetna (AET) president Karen Lynch—No. 21 on this year’s MPW list and a potential successor to the health insurer’s current CEO—echoed a similar attitude. In the running for a senior role, she was told in an evaluation “to avoid wearing pink because it made me look too ‘girlish,'” she tells Fortune. “I was told I was too short, too blonde, and my voice wasn’t deep enough.” She got the job anyway. “Ever since then, I’ve made it a point to wear pink,” she says. “If you are somewhere where you are not recognized and appreciated, find someplace, someone else, who does.”

4. ‘Package’ Yourself

Another important lesson for women? “Just getting the results isn’t going to be enough,” Orr says. Women can’t expect good work to automatically get them noticed as a candidate for promotion. They need to package themselves as a potential CEO—through networking with high-up executives and board members, seeking out mentors and advocates, and acting the part of a leader with team members and subordinates.

“We also just recommend: If you know you have an inkling of that ambition, say it out loud to somebody, because how else would they know?” Orr says.

Lynne Doughtie, CEO and chairman of KPMG U.S. and No. 36 on this year’s MPW list, offers similar words of advice. “Don’t wait for someone to tap you on the shoulder,” she tells Fortune. “Make your goals known and proactively develop relationships with those that can help get you there either in the form of mentors or sponsors.”

5. Be Ready to Say ‘Yes’

Then again, Orr notes, 65% of the female CEOs might never have gotten the job if someone hadn’t tapped them on the shoulder, because they’d never considered themselves eligible before. “But the response is really critical too,” she adds. ‘They needed to be ready to say, ‘Yes.'”

In fact, Stevenson says, many women were so surprised when they were asked if they wanted to be CEO that they answered in the following way: “Hm, I never thought about it. Let me think about it and get back to you.” In several cases, she adds, the women were told, “Don’t ever do that again.” They got the job anyway, but other women might not be so lucky. Don’t make the same mistake: “There is a readiness indicator,” Stevenson says.