He was only the warm-up act for Sen. Barack Obama's economic speech in New York on Thursday, but Mayor Michael Bloomberg sparked plenty of speculation by sharing the stage with the Democratic presidential hopeful.

Obama praised Bloomberg for "extraordinary leadership" and said the billionaire mayor "shows us what can be achieved when we bring people together to seek pragmatic solutions."

A Bloomberg aide said that Obama asked Bloomberg to speak Wednesday and that the mayor didn't want to pass up the opportunity.

Their appearance Thursday comes four months after a breakfast meeting in New York that both politicians were sure to mention.

"Obama and I have to tell you that the reason I bought breakfast is because I expect payback at something more expensive," Bloomberg had said.

Obama joked that he's seeking a steak dinner. But political tongues were wagging about a potential ticket mate -- an idea Bloomberg has dismissed

before. "Nobody is going to ask me to run as vice president," he said in February

Bloomberg, who flirted with the idea of a run for the White House as an independent, said in a February 28 New York Times opinion piece that he would not run for president.

The former Republican, who became an independent while in office, said he had "listened carefully to those who encouraged me to run, but I am not -- and will not be -- a candidate for president."

That decision, coupled with a party switch, fueled speculation that he could endorse a Democratic candidate for the White House.

But political observers say that, for one, Bloomberg doesn't represent a region of the country that a Democrat or a Republican would need. And they don't see him as "No. 2."

"[It's] hard to imagine Mike Bloomberg ... who built a multibillion-dollar corporation of great success, as the VP of anything," Democratic strategist Hank Scheinkopf said.

A Cabinet position such as Treasury secretary could be an option, observers say, but he'd have to support someone first.

"I have not endorsed a candidate, but I've been very clear it's my hope that all the candidates will explain in detail how they will handle the great challenges facing our country," Bloomberg said.

A Bloomberg spokesman says Sens. John McCain and Hillary Clinton have also reached out to Bloomberg after he said he wouldn't run and might endorse someone.

Observers say a Bloomberg stamp of approval would help any of them on economic issues. And the attention keeps the issues he cares about on the table.