Traders however appeared more inclined to spend money on protective trades than on bets looking to profit from a large move to the upside.

About 55,000 contracts were traded in the first two hours of trading, at twice the usual pace, according to options analytics firm Trade Alert.

While both calls and puts were busy traders appeared to be leaning towards bearish bets. Call options are typically bought by investors who believe a stock will rise in value and puts are generally used to hedge against a dip.

"It does appear that there is some defensive positioning going into the announcement," said Dan Deming, managing director at KKM Financial in Chicago.

Alphabet is the last of the group of high-growth tech stocks including Facebook Inc, Netflix Inc and Amazon.com Inc, that together make up the "FANG" group, to report earnings this quarter.

Shares of two of this group have had large post-earnings moves. Amazon shares fell 7.6 percent on the day after it reported results, while Facebook shares jumped by twice as much.

Traders' expectation for a large near-term move in Alphabet shares is high. The 30-day implied volatility, a gauge of the risk of large moves in a stock, is at 37.4 percent, higher than 92 percent of the readings over the last year, according to Trade Alert.

The cost of a straddle in Google's options, a strategy in which a trader buys an at-the-money put option and a similar call option, implied a move of about 6.9 percent in either direction by Friday. Over the last eight earnings reports, the average one-day move after reporting is 5.5 percent.

On Monday, put contracts betting on Google class A shares falling below $660 by Friday, down about 14 percent from the current price, was the busiest option with 1,440 contracts traded.

On the other hand, calls on the shares climbing to $900, up 17 percent by Friday were also busy, with 1,100 contracts traded.

(Reporting by Saqib Iqbal Ahmed; Editing by Meredith Mazzilli)