Option bulls are bombarding Groupon Inc (NASDAQ:GRPN - 5.61) today, with speculators gambling on more gas in the tank for the coupon concern. In afternoon trading, the stock has already seen roughly 36,000 calls cross the tape -- more than three times the norm, and around six times the number of GRPN puts exchanged.

Most active by a mile is the February 5.50 call, where close to 14,900 contracts have traded on open interest of fewer than 13,100 contracts, pointing to fresh positions. Plus, a healthy majority of the calls have changed hands at the ask price, hinting at buyer-driven volume.

More specifically, the soon-to-expire calls have traded at a volume-weighted average price (VWAP) of $0.19, meaning the buyers' profit will increase the higher GRPN exceeds $5.69 (strike price plus VWAP). Earlier today, the shares topped out at $5.71, but have since given back a portion of their lead. Nevertheless, even if GRPN retreats beneath the $5.50 level before options expiration on Friday, the most the speculators are risking is the premium paid at initiation.

From a broader sentiment perspective, today's appetite for calls merely echoes the growing trend seen on the major options exchanges. In fact, the stock sports a 10-day call/put volume ratio of 10.28 on the International Securities Exchange (ISE), Chicago Board Options Exchange (CBOE), and NASDAQ OMX PHLX (PHLX). Not only does this ratio indicate that traders have bought to open more than 10 GRPN calls for every put during the past two weeks, it also stands just 7 percentage points from a 52-week peak. Or, in simpler terms, option buyers are initiating bullish bets over bearish at a near annual-high clip.

As a result, the security's Schaeffer's put/call open interest ratio (SOIR) sits at 0.53, indicating that calls nearly double puts among options with a shelf-life of three months or less. Even more telling, perhaps, this ratio ranks in the sixth percentile of its annual range, suggesting near-term options traders have rarely been more call-biased during the past year.

At last look, GRPN is up 6.1% to explore the $5.61 level, courtesy of an upgrade to "buy" from "neutral" at Sterne Agee.