There are two types of taxes that you see at the pump. Sales tax (if your state has it) and a per gallon tax.
In California, there is 18 cents per gallon plus a 6 percent sales tax. In addition, there is an 18.4 cent federal tax.
California residents pay roughly 36.4 cents per gallon, plus another 25.5 cents per gallon sales tax (at sale price of $4.25 per gallon) for a total per gallon tax of about 62 cents per gallon.
On a typical 16 gallon fill-up costing $68.00, $9.92 is tax paid at the pump.
http://www.californiagasprices.com/Tax_Info.aspx
Actually, in California, the state sales tax on gas is 2.25%.
The excise tax per gallon went up 17.3 cents and the sales tax went down July 1, 2010.
Per the State Board of Equalization:
3. How does the Gas Tax Swap apply to motor vehicle fuel?
Beginning July 1, 2010, the retail sale of motor vehicle fuel is partially exempt from sales and use tax. The partial exemption applies to 6 percent of the current state sales and use tax rate. Therefore, retail sales on or after July 1, 2010 are subject to sales and use tax at a rate of 2.25 percent plus applicable district taxes.
Additionally, beginning July 1, 2010, the state excise motor vehicle fuel tax goes up by 17.3 cents ($0.173) per gallon. As of July 1, 2010, the new state excise motor vehicle fuel tax rate is 35.3 cents ($0.353) per gallon.
http://boe.ca.gov/sutax/gasswapfaq.htm