Toyota Camry [0] Dual VVT-i engine gets 7.9L/100km and 183gm/km emissions. That roughly works out as 2.3kg CO2 per 1L petrol.
Therefore, a tonne of CO2 is produced for every ~430L petrol. Petrol is around AUD $1.40/L, so about AUD $600 of petrol.
Carbon credits [1] are worth about $14 euros per tonne of CO2, which is say AUD $19.
Therefore 'carbon neutral' petrol adds about AUD$20 to AUD$600 worth of fuel, or about 3-4%.
Sound about right? I could stomach that, considering the fuels price goes up and down all the time anyway...
[0] http://www.toyota.com.au/camry/features/economy-and-environm...
[1] http://www.goldstandard.org/blog-item/carbon-pricing-what-ca...
EDIT: formatting...
(This page confirms Toyota's number: http://www.eia.gov/tools/faqs/faq.cfm?id=307&t=11 )
The answer, which took me far too long to realize, is that the oxygen pulled from the air makes up the bulk of the mass of the CO2. Oxygen has an atomic mass of ~16 to Carbon's ~12, which means that 1kg of pure carbon can be combined with oxygen to produce ~3.7kg of CO2.
So yes, your calculations sound about right. Contrary to my first impression they do not violate the law of conservation of mass.
You can start paying off your CO2 right now. This is a side project of mine: https://earthboost.org
Of course, it relies on there actually being a cap on carbon in the first place...
[0] https://en.wikipedia.org/wiki/Carbon_credit#How_buying_carbo...
The person behind the cash register could even ask, "Would you like to make your 'gas/petrol/fuel' today carbon-neutral for an extra $2.45?".
I can see that working with very little capital. It gets sold the same way as the Snickers bars next to the checkout.
Most people don't want to spend any extra money on things that they won't directly benefit from.
This is how organic food started with Whole Foods. And the same strategy could work here.
It won't work to use that angle for gas. Pure environmental plays are harder to find. There are people who pay more for renewable generated electricity, so that's a good parallel. I don't know what percentage, however, or if it'd be enough to support a chain of expensive gas stations.
Also by being high end, theres opportunity to be very different. These stations shouldn't even look like traditional stations. They could provide services that appeal to affluent markets and provide good profit margin. This will be necessary at first because raising gas price alone won't be enough to cover costs.
Everyone that I know that eats organic does it because they believe the food is better for their health.
From what I see, relying on good intentions doesn't quite seem get us to where we need to go.
(this is a submarine comment, I don't want Yoshi to go out of business or I'll have to inflate my own tires again)
Or, well, you could buy carbon credits…