Jay S. Sidhu sparked a rally in Sovereign Bancorp Inc.'s share price Thursday, when the bank chairman told an audience of investors: "We have decided that going it alone is not an option."

Over the next few hours, Sovereign shares spiked up 6 percent, even though Sidhu was only making explicit what bank-watchers already believed: Banco Santander's investment this year in Sovereign is likely to end with Sovereign's eventual sale, at a price more attractive than its recent per-share level in the low $20s.

What's harder to explain is Friday's 6 percent jump in shares of Commerce Bancorp Inc., the other major banking company with headquarters in the Philadelphia area, at a time when bank stock indexes and other major banks, including Wachovia Corp. and PNC Financial Services Group, showed little price change.

Like those of Sovereign and other major bank stocks, Commerce shares have been sleepy lately because, analysts believe, the combination of rising financial costs and flat loan rates will keep squeezing profit.

In the days before its stock rose, analysts at A.G. Edwards, Ryan Beck & Co., Boenning & Scattergood, and other investment firms cautioned clients not to expect much from Commerce shares anytime soon.

Why did Commerce jump anyway? Some bankers and investors noted that Sovereign's disappearance from the local scene would make the surviving banks more attractive to pricey takeovers - and Commerce is the only locally based bank to approach Sovereign's size.

Sovereign, of Wyomissing, Pa., is the second-largest bank based in Pennsylvania, with $69 billion in loans, investments, and other bank assets. Commerce, of Cherry Hill, is the largest bank based in New Jersey, with $44 billion in assets, according to the Federal Deposit Insurance Corp.

Still, Commerce would be a tougher takeover target than Sovereign, said Wilson L. Smith, an analyst at Boenning & Scattergood, in West Conshohocken.

"Sovereign is built to be acquired," Smith said. "It's got your usual bank structure. Buy it, cut it, integrate it, you're done. Commerce has a different sales culture. It would be much more difficult to mesh that culture into a Wachovia Bank or a Bank of America," or another big acquirer.

So what is Smith's explanation? He agrees that scarcity drives up demand, and prices. But he said his colleagues on the Boenning options desk noted that a string of Commerce stock options contracts expired last week, increasing investors' demand for shares to cover previous bets, "and that's usually good for at least a little bump in the price."

Shares in Sovereign rose 2 cents, to $21.56, yesterday on the New York Stock Exchange. Shares in Commerce fell 46 cents, or 1.3 percent, to $35.69.

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