There are various circumstances under which CEOs leave a company -- especially those who have held the position for a relatively long time. At Chevron (NYSE:CVX), the second-largest U.S.-based oil and gas producer, the newly announced resignation of its top man, David O'Reilly, at year's end appears to engender wishes that, given the job he's done, he might remain a bit longer.

After all, Mr. O'Reilly, at 62, is still three years short of his company's mandatory retirement age. And after a decade at Chevron's helm, he has a number of accomplishments to point to. But then, the company appears to have a capable successor in John Watson, who, during a nearly 30-year career with Chevron, has become Mr. O'Reilly's confidant -- along with carrying the more formal title of Chevron's vice chairman.

Perhaps Mr. O'Reilly's most noteworthy accomplishments were a pair of significant acquisitions. I'm referring to the 2000 purchase of Texaco, which set Chevron back $35 billion. And then in 2004, Chevron spent $18 billion to buy Unocal, which at the time was being chased by Chinese offshore oil company CNOOC (NYSE:CEO).

And just recently, the final go-ahead for the massive Gorgon gas project in Australia, in which Chevron has a half interest and of which it is the operator, was received. ExxonMobil (NYSE:XOM) and Shell (NYSE:RDS-A) share the remaining Gorgon interest.

But the company has had to clear some hurdles as well, including the nationalization of energy in Venezuela, which stripped half a dozen big oil companies, including Statoil (NYSE:STO), Total (NYSE:TOT), and BP (NYSE:BP), of their Orinoco basin operating positions before turning those positions over to PdVSA, the nation's state oil company.

And then there's a pending lawsuit in Ecuador that may be completed before Mr. O'Reilly's departure. The suit attempts to hold Chevron accountable for purported environmental damage by Texaco long before its acquisition by Chevron.

But all in all, Chevron appears to be in excellent condition. It expects to cease U.S. natural gas drilling by year's end in the face of current the glut of hydrocarbon. But beyond that, it's busy uncovering oil and gas across the world with an anticipated production growth of 5%, better than even Big Oil top dog Exxon.

While Mr. O'Reilly was born and educated in Ireland and came up through the engineering ranks, Mr. Watson is a financial type. However, it's difficult to image that the company will change appreciably once the torch is passed. To my way of thinking, Chevron will continue to be a well-run company that is deserving of Foolish attention.

Chevron wears four stars as awarded by Motley Fool CAPS players. I suggest you add your assessment of the company.

Fool contributor David Lee Smith doesn't own shares in any of the companies mentioned. He does welcome your comments. StatoilHydro ASA and Total SA are Motley Fool Income Investor selections. CNOOC is a Motley Fool Global Gains recommendation. Try any of our Foolish newsletters today, free for 30 days. The Fool's disclosure policy doesn't plan on retiring anytime soon.