Their opposition to cap-and-trade intensified when they weren't granted liberal exemptions under the greenhouse gas bill that passed the House last summer -- the bill that this Senate version is meant to complement.
So to win their support the Senate proposal is thought to include a straight-up carbon tax on products derived from oil, such as gasoline, which would likely be passed along to consumers at the pump.
The tax isn't expected to be huge -- starting at something under 10 cents a gallon for gasoline and moving up to maybe 20 cents a gallon after 10 years, said Kevin Book, Managing Director of research at ClearView Energy Partners, a Washington D.C.-based research firm.
And the tax isn't expected to discourage people from driving, said Book, as it's too gradual and small to have much of an impact. But revenue from it would likely be spent on other, cleaner transportation projects like mass transit or subsidies for hybrid cars.
20 cents over 10 years is well below any estimates I've seen for an efficient gas tax (most estimates I've seen have been in the neighborhood of $1 per gallon). Now I know why Exxon favors a tax over cap and trade.