NEW YORK (CNNMoney.com) -- Corporate women made impressive strides in 2006, taking charge at a slew of giant companies, and bringing in big paychecks to boot.

The top-earning woman executive is Safra Catz, president and CFO of Oracle (Charts), who took home a cool $26.1 million in total compensation last year, according to Equilar, Inc., a San Mateo, Calif.-based compensation research firm, which calculated the results for Fortune magazine. Second-highest paid is Susan Decker, CFO of Yahoo! (Charts), who brought in $24.3 million.

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Handsome sums indeed, but not nearly enough to land them on Fortune's list of 10 highest-paid executives overall.

The 10 execs who enjoy that distinction each collected more than $48 million in total compensation last year - much of it coming in the form of restrictive stock or stock options - and all of them are men.

No. 1 earner Eugene Isenberg, CEO of Nabors Industries (Charts), brought home $71.4 million in 2005, according to Equilar. Other members of the top 10 include Occidental Petroleum (Charts) CEO Ray Irani, who made $70 million; Yahoo chairman and CEO Terry Semel, who earned $56.8 million (more than double CFO Decker's pay); and Oracle CEO Larry Ellison, who made $52.3 million (double what Catz, the company's president and CFO, took home).

The lowest-earning of the 10 best-compensated male execs is James R. Moffett, who was paid $48 million as chairman of the board at Freeport McMoRan Copper & Gold - nearly 85 percent more than the top-earning woman.

So in a year Fortune is calling the year of the Most Powerful Woman CEO, why the striking difference in paychecks?

"All through the pipeline women leaders aren't paid as well as men," said Lois Joy, research director at Catalyst, a nonprofit that seeks to advance women in business. "And when you get to the CEO level, that same inequality is replicated."

Indeed, the earnings of women in full-time management and professional jobs last year averaged 73 percent of men's, according to the Bureau of Labor Statistics. That gap can be explained to a large extent by nondiscriminatory factors, some studies have found, and are based on a division of labor in the home that relies more heavily on women than on men, according to Catalyst.

Women are not only less likely to work continuously during their lives, but responsibilities at home also influence their choice of job and type of employer, Catalyst said.

But such factors probably weigh less on the elite corporate women on this list. Four of the best-paid female executives also appear on Fortune's 50 Most Powerful Women list this year. They include Morgan Stanley's Zoe Cruz, who made $21.1 million in 2005; Genentech's Susan Desmond-Hellmann, who took in $17.1 million; eBay's (Charts) Meg Whitman, who pulled down $16.2 million; and Avon's (Charts) Andrea Jung, who earned $11.6 million.

And Catz, the top-earning woman, is making 36 percent of what the No. 1-ranked male executive, Isenberg, earns - a far bigger gap than the 73 percent managers and professionals overall experience. So what gives?

CEO paychecks include so many items, including stock options and bonuses that are open to negotiation - that the sheer magnitude of sources can increase the potential for inequality and worsen the gender gap, Joy explained.

On top of that, "there's a lot more money to play around with," she said.

Another factor is that 2005 was such a stellar year for the oil and gas, and commodities industries. Executives at three oil and gas (Nabors, Occidental Petroleum, and Exxon Mobil) corporations appear on Fortune's 10 highest-paid list, and the size of their executives' mega paychecks were mostly thanks to the value of their stock options and restricted stock awards. Meanwhile, at commodity company Freeport McMoRan, options and a hefty $19 million bonus were responsible for most of Moffett's pay.

But while industry performance played a role, it doesn't account for all the paycheck differences at the top - or why would Barry Diller be bringing in $62.3 million as head of IAC/Interactive (a company with $7.1 billion in revenues) to Meg Whitman's $16.2 million as head of eBay (which has $4.5 billion in revenues)?

At lower levels, a lot of the disparity between executive men and women's paychecks can be explained by the fact that women managed smaller companies and were less likely to be CEO, chair or company president, said Kevin Murphy, a professor at USC's Marshall School of Business citing a paper by Marianne Bertrand & Kevin Hallock.

In fact, eight out of 10 of the highest-paid executives overall are CEOs, while only five of the 10 best-compensated women are chief executives. To determine the 10 best-paid women and executives overall, Equilar looked at companies with more than $1 billion in revenues that filed proxies as of Sept. 1. They included base salary, bonuses, the present value of option grants, restricted stock awards, long-term incentive-plan payouts, and other compensation as disclosed in company proxies.

After that is taken into account, since there are so few women CEOs in general, "chances are you are not going to find any women in the top 10 [paid]" Murphy noted.

"Forget the fact that they are paid less, the big picture is the scarcity of women executives," Murphy said.

Next: 50 Most Powerful Women

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