Port of Oakland Executive Director Omar Benjamin was placed on immediate paid administrative leave Thursday, after allegations that one of his top aides spent $4,500 in public money at a Houston strip club.

Benjamin, who has been head of the port since 2007, was placed on leave by the Board of Port Commissioners after a lengthy closed-door session Thursday evening.

As director, Benjamin oversaw the port's maritime operations, Oakland International Airport and its commercial real estate.

The commission named Deborah Ale Flint, the port's director of aviation, to take the helm for the time being.

No reason was given for Benjamin's removal, but the commission also announced it is bringing in an outside law firm to review credit card expenditures by port brass.

"We continue to take this situation very seriously," Port Board Commission President Gilda Gonzales said in a news release. "Holding those responsible accountable is our highest priority."

Benjamin's exit comes after The Chronicle reported that port Maritime Director James Kwon allegedly spent $4,500 entertaining shipping executives at Treasures, a Houston strip club, during a business conference in 2008.

According to a well-placed source, port commissioners were told that the strip-club trip may be the tip of the iceberg and that the port was looking at the possibility that there may have been "hundreds of thousands of dollars in questionable expenditures" by higher-ups going back several years.

There are also rumors swirling around port headquarters that Kwon may not have been the only port executive at the Houston strip club.

Kwon has been on a business trip in China and has yet to comment.

In a statement Thursday night, Oakland Mayor Jean Quan, who was at a conference in Denver said, "I expect the Port Commission to thoroughly investigate these matters and hold all responsible parties accountable. That is why I fought hard to appoint stronger commissioners with financial and business expertise."