Well their 33% is much higher than our current 3% and our whopping 5% maximum capacity using untapped reserves. We would have practically no effect on oil prices and it could be easily wiped out with a 2% OPEC reduction.
Sure they have some effect and the world would be in deep dodo if they cut back drastically. But in the long term they risk having their best customers switch over to alternate forms of energy and losing them forever. It doesn't seem possible, but Israel is trying to get completely off oil. It would be a little a more difficult here in the US, but we could incorportate many of their ideas and just use gas for longer haul transportation.