NEW YORK (Reuters) - An unusually large number of bullish bets were placed on the options of Sapient Corp. (>> Sapient Corporation) just three days before the digital ad specialist announced plans to be acquired for $3.7 billion by French advertising giant Publicis (>> PUBLICIS GROUPE), according to options market data.

Sapient shares jumped 43 percent to $24.73 on Monday after the company said it would be acquired by Publicis. The jump in the stock would result in big paper profits for some well-timed options bets last week, options strategists said.

Sapient's options are usually very thinly traded with daily contracts volume of less than 100 for most days this year.

Starting Oct. 6, however, trading in the options started showing increased activity, most of it in calls - typically used to make bullish bets on a stock.

Sapient's 30-day implied volatility, a measure of the risk of large moves in a stock, also jumped 32 percent to 55.12 percent on Oct. 29.

"I would say that the jump in option prices on Oct. 29 is very unusual, and could indicate that information about this merger was revealed in the markets before the official announcement," said David Hait, president of OptionMetrics in New York.

Between Oct. 29 and Oct.31, 6,851 calls and 1,082 puts were traded on Sapient's options, according to options analytics firm Trade Alert data.

Calls betting on Sapient shares rising to $17.50 by Nov. 22 and others banking on the shares hitting that level by Dec. 20 were among the most popular options and with volume of 1,609 and 771 contracts, respectively, according to Livevol Inc data.

"Just based on this activity, it seems like some investors were expecting some sort of catalyst to move the stock. It is a sign that some sort of news was anticipated," said WhatsTrading.com options strategist.

With Monday's share rise, the premium paid for Sapient calls at the $17.50 strike price and set to expire on Nov. 22, rose $5.40 to $7, according to Thomson Reuters data. The premium on calls at the $17.50 strike and set to expire on Dec. 20 was up $5.39 at $7.24.

“Someone is definitely making a lot of money on this and they were buying the calls right before the merger was announced,” said optionMonster.com lead analyst David Russell.

A spokeswoman for Sapient declined to comment on the unusual options activity.

(Reporting by Saqib Iqbal Ahmed; additional reporting by Jennifer Saba; Editing by Cynthia Osterman)

By Saqib Iqbal Ahmed

Stocks treated in this article : PUBLICIS GROUPE, Sapient Corporation