Mesa Petroleum Co. Chairman T. Boone Pickens Jr. yesterday gave a new Mesa stockholder the type of welcome Pickens himself would like to receive for a change.

Baupost Group Inc., an investment adviser in Cambridge, Mass., said in a filing with the Securities and Exchange Commission that it has purchased a 5.72 percent stake in Mesa. Baupost said the Mesa shares "are being held for investment purposes."

"We will be glad to hear any ideas they might have," Pickens said. "Our reaction to it is they are large stockholders, and we are in communication with them. It would surprise me if we didn't get along well. They want us to maximize shareholder value, and that is exactly what we want to do also."

When Pickens has notified the SEC of his initial stakes in major oil companies, including Gulf Oil Co. and Unocal Corp., the targets of his affection have not responded so warmly. Fearful that a hostile takeover bid would follow Pickens' stock purchases, executives at these oil giants have made it clear that they would be happier if Pickens invested his time and money elsewhere.

Why did Baupost buy the Mesa stake? Not because of Mesa's oil and gas assets. Those were spun off to a separate partnership last year.

Ironically, the asset that caught Baupost's attention was Mesa's ownership of 14.6 million Unocal shares, about 13 percent of Unocal. That $350 million of securities is Mesa's main asset. Depending on how you view the tax laws, it may be cheaper to buy an interest in Unocal through Mesa than through the direct purchase of Unocal shares, according to Seth A. Klarman, vice president of the Baupost Group.

"For the long-term investor, at the right price this has considerable investment merit," Klarman said. "I would say currently the assets of Unocal are available through Mesa common stock for a discount price ." How did Mesa respond to Klarman's interest?

"Their attitude has always been that the stock is public and they care less who owns it ," Klarman said. "They're delighted someone else perceives value. We bought this totally for investment purposes without any other intentions."

Pickens has been accused in the past of filing documents with the SEC that said his stock purchases were "for investment purposes only" and then altering the filings just before launching a hostile takeover bid. Is Pickens worried that Baupost may follow his lead?

"They tell us this is for investment purposes only, and I have no reason not to believe that," Pickens added.

Wall Street doesn't doubt Baupost either. Despite Baupost's filing, Mesa stock dropped 12 1/2 cents to $2.38 yesterday.