That's exactly when you get these short term selloffs. What happens is that speculators/traders buy on the expectation of a particular short-term outcome, and as soon as they get that, they sell. I'm not exactly wishing for that outcome as I'm sitting on a bunch of OEX calls bought yesterday, but this frequently IS the way this thing works. But with options expiration on Friday and the bulls with the winning hand, they may seek to push their advantage (this means professionals buying futures contracts to push the market in that direction for a day or two, then they close those positions immediately, and you get a big drop on Monday). Either way, I think the winning traders will want to book their profits soon, and unless there are some institutions doing exactly what I'm doing (an anticipatory hedge ahead of acquiring longer term positions) you will get some kind of selloff.