I get it, but at this point there is less worldwide demand, OPEC is trying to compete with new markets including our own domestic production, and there are a bunch of other factors pointing to oil prices per barrel staying down for a while. If domestic companies raise their prices, they'll price themselves out of the current very low market (which may well be willing to go even lower). At the moment, economically, this tax would have them over a barrel, if you'll pardon the pun.
At least I think that's the theory. These things are never all that elegant in application.