By Jud Pyle, CFA, chief investment strategist for the Options News NetworkCHICAGO -- Crude oil took its biggest hit in three months yesterday, dropping nearly 6% to $63.26 a barrel the same day U.S. durable goods orders dropped by 2.5%. But at least one investor expressed bullishness with a tall order of calls in the United States Oil Fund ETF ( USO) during afternoon trading. The investor bought 100,000 Jan. 2010 55 calls for 25 cents per contract, with the stock trading around $33.80. That means this investor needs USO shares to expire higher than $55.25 in half a year. These calls dropped three cents on the day and were home to open interest of 3,100 contracts. By the end of the day, more than 105,000 Jan. 55 calls changed hands, and USO shares closed down $2.29 to $33.47. It's interesting that we saw heavy call-buying activity after USO stock has seen a prolonged downturn since the end of September last year -- these shares have dropped 71% since reaching a 52-week high of $117.24 last July. While investors should not interpret bullish activity such as this as a reason to buy up USO stock, it is interesting that at least one investor bought calls in this fund on a down-market day. Jud Pyle is the chief investment strategist for Options News Network and the portfolio manager of TheStreet.com Options Alerts. Click here for a free trial for Options Alerts. Mr. Pyle writes regularly about options investing for TheStreet.com.