In most EU states, there are VAT exemptions for the fuel used in domestic and intra-EU flights, while no similar exemptions exist for the fuel used in trains (and cars). Likewise, there exist VAT exemptions for plane tickets.

At least in Portugal, querosene is also exempt from the ISP (tax on the petroleum products). VAT and ISP make up more than half of the retail price of diesel and is almost 2/3 of the price of gasoline. Interestingly, the VAT rate of 23% is applied to the price with ISP included. So you effectively pay a tax on the tax. Finally, there's the fact that we're emitting free 2009/29/EC directive carbon allowances for aviation.