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.