measuring co2 (cars particularly)

I found this stuff on this site

has anyone else got other info that verifies or varies dramatically from this?
i want to use some numbers that are generally considered accurate. my wife showed me some info from a certain extremist group .. anyhow.. and im quite sure its pie in the sky numbers used to suit their needs. what do you think of these numbers from the above site:




Auto Travel
The calculation for auto travel works differently depending on whether you choose to enter you own annual miles driven, and your own miles per gallon, or you choose to use national averages.

The first step is to enter the miles per gallon for your vehicle (let's say 25), or choose a national average MPG for either cars (21.4), or SUVs (17.1)5.

Then either enter the your own annual miles driven (let's say 10,000), or choose the national average (11,904 )6.

The calculator then divides your annual miles driven (10,000) by your miles per gallon (25).

10,000 divided by 25 = 400 gallons of gasoline per year.

The calculator then multiplies your gallons per year (400) by the CO2 per gallon of gasoline (19.564)7.

400 multiplied by 19.564 = 7,826 lbs. of CO2 per year.