Roll-up giant United Rentals Inc. has hung a “For Sale” sign on its front door as part of an executive-level reshuffling.

United’s board of directors announced in a regulatory filing and press release on April 10 that the rental operator is exploring “a broad range of strategic alternatives...including a possible sale of the company.”

The world’s largest rental company also noted that chief executive Wayland R. Hicks plans to retire at the company’s annual shareholder meeting on June 4.

Michael J. Kneeland, who is chief operating officer, executive vice president and an aerial work platform guru, will succeed Hicks as interim chief executive. Kneeland joined the company in 1998. Hicks plans to stay on the board of directors along with Chairman Bradley S. Jacobs.

The company apparently is in a quiet period as it meets with financial advisers about its next steps. Officials did not return ENR’s phone calls.

Some industry insiders have speculated that United is a potential target for private-equity bidders, who have recently been snatching up rental firms in a time of healthy profits.

“There’s a lot out there and a lot that have invested in the rental ‘game’ recently,” says Frank Manfredi, an equipment analyst in Mundelein, Ill.

United’s announcement comes after a string of recent sales of other national rental firms, such as Hertz, RSC, NationsRent and Neff.

Greenwich, Conn.-based United earned net income of $224 million last year, up 19.7% over 2005, on sales of $3.64 billion. United has forecast an overall 16.2% to 20.6% earnings-per-share increase in 2007.

Rental rates also increased 5.3% for the full year from United’s $3.9-billion rental fleet.