H.R.6000: To amend the Internal Revenue Code of 1986 to impose a windfall profit tax on oil and natural gas (and products thereof) and to allow an income tax credit for purchases of fuel-efficient passenger vehicles, and to allow grants for mass transit.

Gas Price Spike Act of 2008 - Amends the Internal Revenue Code to impose a windfall profit tax on crude oil, natural gas, or products of crude oil or natural gas. Defines "windfall profit" as so much of the profit on a sale of crude oil, natural gas, or related products as exceeds a reasonable profit. Establishes the Reasonable Profits Board to determine levels of reasonable profit from the sale of such products.

Allows a tax credit for the purchase of certain fuel-efficient, American-made passenger vehicles.

Authorizes the Secretary of Transportation to make grants to operators of mass transit systems, including bus and commuter rail systems, to reduce passenger fares on such systems.