Assuming a 45 liter tank you'd spend €84.60. Mind that a LOT of that is tax. If you strip off Value Added Tax -- equivalent to sales tax if I understand correctly, though a fair bit higher -- you'd pay €70.50. That still leaves excise tax, which is levied specifically on goods the government wants to discourage. Cigarettes, Alcohol, Gas. Without that you'd pay €34.99.
I'm not sure how the tax breakdown works in Texas, but I'd not be surprised if it'd be one of the main drivers of the price difference.
But it it provides vast amounts of energy. The US gov cares about different things.