Quote from segv:
If you are an American you pay income tax on every form of income worldwide. This includes income from options, futures, forex, guns, drugs, smuggling, gambling, and acts of god. For an American, if you have to ask, the answer is "yes". The type of tax paid depends on your tax status with the form of income in question. For example, you might normally pay 60/40 long/short capital gains tax for section 1256 contracts, or ordinary income if you have made the mark-to-market election. Talk to an accountant.