UPDATE 2-Rowan would mull leaving U.S. as part of M&A plans

* Rowan eyes ultra-deepwater, high-end jackup rigs - CEO

* To weigh potential incorporation outside United States

* Expects jackup retirements to help market in next decade

* Sector leader Transocean takes four rigs off the market (Adds CEO quotes, Transocean rig update, byline)

By Braden Reddall

SAN FRANCISCO, Feb 2 (Reuters) - Rowan Companies Inc (RDC.N), seeking a lower tax rate like its rivals, would try to rebase outside the United States as part of any deal to expand its oil and gas rig fleet, its chief executive said on Tuesday.

In the years ahead, Rowan wants to buy some ultra-deepwater rigs and also strengthen its grip on the market for high-end jackup rigs, their shallow-water counterparts, CEO Matt Ralls told the Credit Suisse Energy Summit in Vail, Colorado.

"As we look at these expansion opportunities, one of the things we look at is the ability to get us re-domesticated in that transaction," Ralls said, though he added there was "nothing imminent" in terms of mergers or acquisitions.

Shares of Rowan climbed 2 percent to close at $22.69 on the New York Stock Exchange.

Rowan's operational headquarters are in Houston, and it is incorporated in Delaware like many U.S. companies.

Larger rivals in recent years have moved their corporate homes out of the United States so they could pay less taxes.

In late 2008, sector leader Transocean Ltd (RIG.N) moved its headquarters to Switzerland for tax reasons and to get closer to its customers, followed months later by Noble Corp (NE.N), the third-largest rig contractor by market value.

Ensco International Plc (ESV.N), the fourth-largest U.S.-listed offshore rig contractor, has just completed a move to London for the same reasons.

Ralls, who joined Rowan last year after serving as chief operating officer of GlobalSantaFe before Transocean bought it in 2007, said the Middle East and Southeast Asia looked to be the strongest areas for high-end jackups at the moment.

He said persistent concerns surrounding the global jackup market were overdone, since nearly half of the 61 new rigs due to be delivered in the next three years were headed to non-competitive markets or had inadequate financing.

Adding that customers increasingly wanted newer and more capable rigs, he also noted that three-quarters of the 457 jackups worldwide were more than 20 years old.

"Time favors the jackup operators because the average fleet age is so old," Ralls said, pointing to industry estimates showing the global fleet would grow over the next few years before falling back below 450 by 2018 as rigs were scrapped.

Transocean, the world's largest offshore rig contractor, has sought to help bring the jackup market into balance by stacking, or setting aside, many of its rigs.

On Tuesday, the company said it stacked two more jackups, including one in Egypt that entered service in 1969 and another in Malaysia that started work in 1982. It also said it stacked two floating rigs in Africa that entered service in the 1970s.

(Reporting by Braden Reddall; Editing by Robert MacMillan and Richard Chang)