Powerline has done us all a service by pointing out that when government makes a prediction about how much drilling in a particular area will yield, they start with a prediction of what price the oil will command. In the case of the "ANWR and offshore drilling will only produce 200,000 barrels annually" and "it won't reduce the price of gas much," they've deliberately assumed that the price of crude oil will plummet.
Now, I will certainly be glad to have lower fuel bills, but the fact of the matter is that this is a classic example of "garbage in, garbage out." As long as estimates of fuel costs vary wildly from what actually happens, we need to ignore these prognostications and fall back on what we should know from Econ 101: when supply increases, the market price decreases, all else the same.
I'll be expecting the left side of the aisle to figure this one out about the same time they figure out that "controlling the supply of petroleum" is NOT among the enumerated powers of Article 1 of the Constitution.