Clorox shares rose the most in two years after a trader bought bullish options and investors speculated Colgate-Palmolive will make an offer for the maker of bleach and laundry detergent.

About 2,900 calls expiring in July with a $95 strike price were purchased in New York, according to Trade Alert, a New York-based provider of options-market data. Shares of Oakland-based Clorox jumped after the transaction, rising as much as 4 percent, the biggest increase since September 2011.

"This is a relatively big trade in a name that doesn't trade much," Anshul Agarwal, an equity derivatives strategist at Bay Crest Partners in New York, said in an interview. "It appears definitely that the investor is expecting an announcement soon."

Other large purchases included 1,000 July $92.50 calls and 1,000 June $90 calls. The trades happened in a 20-second window and it's unclear whether more than one person made them, Henry Schwartz, president of Trade Alert, said by phone.

The stock closed up 3.5 percent to $92.66. More than 26,000 calls changed hands, the most since January 2013, according to data compiled by Bloomberg. That compares with average daily volume of 372.

Investors exchanged 15,300 of the $95 call options expiring in July, boosting the implied volatility, a measure of the cost of options, according to data compiled by Bloomberg.

There is speculation that Colgate, the toothpaste and soap maker, may be looking to strike a deal with Clorox, according to Mark Sebastian, founder of Option Pit LLC, a Chicago-based education and consulting firm. Billionaire Carl Icahn, once the largest investor in Clorox, has advocated for the company to put itself up for sale in the past.

"Colgate-Palmolive would be a great fit for Clorox," Sebastian said by phone. "There are tons of synergies there. Procter & Gamble Co. would be a better fit, but there are regulatory issues."

Clorox spokeswoman Aileen Zerrudo said the company is aware of the increased option trading. She declined to comment on whether Clorox has any pending announcements or on the possibility of combining with Colgate. Tom DiPiazza, a spokesman for Colgate in New York, declined to comment.

Investigators are reviewing large option trades in Clorox ahead of Icahn's attempt to buy the company in 2011, as well as trading by golfer Phil Mickelson and sports gambler William Walters in Dean Foods in 2012, according to a person familiar with the matter. None of the three men has been accused of any wrongdoing.

The jump in Clorox call volume is reminiscent of the increased trading before Berkshire Hathaway and 3G Capital agreed to buy HJ Heinz last year, according to Christopher Rich, head options strategist at JonesTrading Institutional Services.

In April, a New York judge approved a $4.8 million deal between the U.S. Securities and Exchange Commission and two Brazilian brothers, Michel and Rodrigo Terpins, who were accused of using confidential information to make options trades ahead of an announced Heinz deal.

"People remember what happened in Heinz, which was another sleepy, solid, good dividend stock that got a bid in the past," Rich said in an interview. "Shortly before the announcement, there was call buying."