Facebook Inc (NASDAQ:FB - 23.44) call volume was running two times above normal levels on Friday, as bullish investors scooped up relatively short-term positions in hopes of hopping on the stock's recent upsurge. Notably, speculators purchased a December-dated bull call spread, which shoots for moderate upside in the shares over the next month.

A block of 3,700 December 23 calls traded near the ask price of $1.74 each, while a symmetrically sized block of the December 26 calls crossed the tape at the bid price of $0.45 per contract at the same time. Given this morning's open-interest increases at both strikes, it appears traders bought to open the lower-strike, in-the-money call, while selling to open the higher-strike call.

A bull call spread strategy reduces the overall premium paid, but also caps the potential upside, versus a traditional call purchase. In this case, the premium was limited to $1.29, which is also equal to the maximum risk, should FB be trading south of $23 at December options expiration. The maximum potential profit -- if FB is at or above $26 when the options expire -- is $1.71 (difference in strike prices less net premium paid). Breakeven at expiration is $24.29 (long strike plus premium).

This penchant for calls flies in the face of recent activity, which has been tilted toward the put side despite the stock's rebound attempts. At the International Securities Exchange (ISE), Chicago Board Options Exchange (CBOE), and NASDAQ OMX PHLX (PHLX), the 50-day put/call volume ratio stands at 0.98, meaning bought-to-open puts are nearly at parity with calls going back 10 weeks. In the past 10 days, however, this ratio measures 1.69, meaning 169 puts have been bought to open for every 100 calls.

FB has outperformed the broader S&P 500 Index (SPX) by 33 percentage points in the past month -- and by 26 percentage points during the past three months. While still trading at a notable discount from its IPO price, the stock is up roughly 12% in November alone and responded to last week's lockup expiration with a surge higher.