We've been thinking a lot about executive leadership lately, for a number of reasons. A company can have its arms around great assets and plenty of capital in the dugout, but in the end, leadership skills get it to home plate.

In the past few weeks, several noteworthy and long-serving chairmen and chief executives have retired, leaving behind them some remarkable achievements and some controversial, but interesting, legacies and lessons.

The ex-CEO Club now includes J. Larry Nichols, co-founder and former executive chairman of Devon Energy Corp. He built that company from scratch in 1971 to become one of the first mega-independents, through huge corporate acquisitions and daring-do in the deepwater Gulf of Mexico, the Canadian oil sands and offshore Africa.

Also retired is Randy Limbacher, most recently chairman, president and CEO of Rosetta Resources, and who before that helped build a strong legacy at Burlington Resources. Then there's Mark Papa, CEO and chair of EOG Resources. He's been with EOG and its predecessor companies for 31 years, leading a pioneer in the shale and liquids plays. Finally, Jim Hackett, non-executive chairman of Anadarko Petroleum, retires this month, leaving behind one of the most successful domestic and international wildcatters in the mega-indie group.

Already garnering too much ink is Aubrey McLendon, co-founder and CEO of Chesapeake Energy Corp. He built CHK into the second-largest natural gas producer in the US, a strong proponent of natural gas demand, and a leader in uncovering shale plays. He also walked out the door of a company struggling to sell $4- to $7 billion in assets in order to handle its debt. However, his legacy to the company, Oklahoma and the nation is well-documented.

In a sign of the constant renewal this industry affords entrepreneurial spirits, he has already started three new companies, including American Energy Partners, which seeks acquisitions—and, in his words, “I am not afraid of natural gas.”

Meanwhile, the curtain rose on two major boardroom dramas: “A classic in-the-open proxy fight for board control at Hess and a classic cloak-and-dagger chairman vs. CEO intrigue at Occidental Petroleum,” as the Wall Street Journal described it.

Deutsche Bank research analyst Paul Sankey said in a research note, “On balance, we see a win-win situation at Hess, given that existing management is aggressively pursuing restructuring…BUY. At Oxy by contrast, we see a high-risk situation with more limited upside from possible restructuring, or a management-change mess.”

At press time, the Oxy board, under fire for months from activist shareholders, cleaned up the “mess,” and non-executive chairman Ray Irani, 78, said he will retire.

Perhaps it is a good idea to revisit the Chesapeake 12-step program devised by Bernstein research chief Bob Brackett a couple of months ago. “…investors naturally have had a lot of questions about the company's future.The No. 1 question is, 'What would it take for you to view CHK positively again?'”

In a recent report, Brackett outlined 12 steps he thinks the Chesapeake board of directors and its CEO-to-be should take: cut spending to match cash flow, sell assets and cut debt, improve governance and transparency, and so on.

There are other reasons we have been pondering leadership. For several years now, gray-haired pundits have fretted over recruiting the next wave of talent to replace the baby-boomers who will retire soon.

E&P companies are working on this challenge. So too are each of the relevant industry organizations, from the Society of Petroleum Engineers to the Independent Petroleum Association of America. It's working. University enrollments in geology and engineering are up. The IPAA and the Houston Independent School District announced recently they will soon open a petroleum charter high school.

Meanwhile, many younger professionals have already entered the workforce, so we wanted to get to know them better. We asked our readers and editorial sources to identify some up-and-coming E&P leaders who have already made their mark. These are some of the best and the brightest who are leading now.

We are thrilled with the results: Oil and Gas Investor's inaugural 20 Under 40 list. These professionals are seizing the many opportunities available in the upstream oil and gas sector, and they are well on their way.

You can meet some of them at our 6th annual Energy Capital Conference in Houston on June 18, where they will be joined by the winners of our 10th annual Excellence Awards. Speakers include the Executive of the Year, a 20 Under 40 honoree who completely restructured an E&P company to save it, and three seasoned board members who have had to handle the thorny issue of CEO succession planning in recent months.

In the end, it's no surprise. The corner office has to be occupied by someone boasting a multitude of talents: business smarts, ethics, drive, creativity, technical knowledge, financial savvy and endurance.