The Securities and Exchange Commission may consider offering rewards to informants who provide tips on the sources of merger rumors that cause volatile buying and selling of stock, Chairman John S. R. Shad said yesterday.

Shad, in an interview with Cable News Network, expressed concern over the growing problem of explosive stock-trading activity prompted by unconfirmed -- and sometimes unfounded -- speculation about mergers and other important corporate actions.

Last week, Pennzoil Co. Chairman J. Hugh Liedtke asked the SEC to investigate the source of rumors of an agreement between Texaco Inc. and Pennzoil to settle their multibillion-dollar legal battle.

The rumors -- later denied by both sides -- caused a surge of trading in Pennzoil stock on Jan. 7, pushing its price up by 25 percent.

"Some people put out some absolutely false rumors, which they knew were false, and it jacked the price up 20 points," said one source close to the two companies.

A speculator could have bought an option on 100 shares of Pennzoil stock for $37.50 on Jan. 6 and sold it for $1,025 at the close of trading Jan. 7.

The New York Stock Exchange is investigating the Pennzoil trading, and an equally dramatic run-up in stock prices that preceded announcement of a proposed merger between General Electric Co. and RCA Corp. a few weeks ago, according to a spokesman.

An SEC spokeswoman declined to comment on any agency reaction to the Pennzoil request.

But Shad noted the commission's concern about the impact of rumors on the stock market. He said he has asked the SEC staff to consider the possibility of offering rewards to informants.

If the staff does prepare such a proposal, the commission would vote on whether to offer it as a formal proposal and invite public comment. Then the SEC would vote on whether to institute such a system.

Shad said he will also convene a roundtable of experts on Feb. 19 to consider the issue of rumors and stock market manipulation, a problem that some experts say has reached proportions not seen since the 1920s.