For an overview of prices in Europe: http://www.adac.de/infotestrat/adac-im-einsatz/motorwelt/benzinpreis_ausland.aspx http://www.avd.de/wissen/infothek/rund-um-den-kraftstoff/benzinpreise-in-europa/preise-fuer-superkraftstoff
http://www.anwb.nl/vakantie/reisvoorbereiding/brandstofprijzen-europa (Dutch)
http://www.fuel-prices-europe.info/
(English)
For specific locations in Germany: http://www.adac.de/infotestrat/tanken-kraftstoffe-und-antrieb/kraftstoffpreise http://www.clever-tanken.de
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As for France, you can have a look at this governmental site which gives you petrol prices depending on your location and type of fuel :
http://www.prix-carburants.gouv.fr/
You can even set your itinerary and see which gas stations you'll encounter along the way : http://www.prix-carburants.gouv.fr/itineraire/
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Super 95 prices per liter for February 2015: France: 1.37 EUR Netherlands: 1.63 EUR Belgium: 1.40 EUR Germany: 1.38 EUR Italy: 1.65 EUR At least for Germany
I can confirm the prices are still the same right now
(end of March 2015).
source: http://autotraveler.ru/en/spravka/old/fuel-price-in-europe-02_2-2015.html
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Anecdotal advice: If you're heading to the German Alps, note that fuel prices can be noticeably cheaper in Austria.
It could be worthwhile driving across the border for several km if filling-up.
(In some places this is possible without driving on an autobahn.)
Separately: familiarise yourself with European road-tax schemes.
For example, Austria requires drivers to purchase a [multi-day] vignette if travelling on their autobahns.
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For Italy , you can compare prices at different stations on http://www.prezzibenzina.it/ .
Just put a city or street name in the search box.
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I am planning to travel in Europe (France, Netherlands, Belgium, Germany, maybe Italy) by car. The price of petrol can be significantly different from country to country, and sometimes even between petrol stations in the same country.  Is there a resource that lists and compares prices for different countries and different petrol stations?  (note: resources for other countries are welcome. It may help other users)
Petrol price comparison in Europe. Which resources are there?
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Different comparison websites for Europeinclude http://www.adac.de/infotestrat/adac-im-einsatz/motorwelt/benzinpreis_ausland.aspx  http://www.avd.de/wissen/infothek/rund-um-den-kraftstoff/benzinpreise-in-europa/preise-fuer-superkraftstoff, http://www.anwb.nl/vakantie/reisvoorbereiding/brandstofprijzen-europa (Dutch) or http://www.fuel-prices-europe.info/. Fuel prices can be significantly cheaper in Austria, but Super 95 prices for February 2015 were:    France: 1.37 EUR  Netherlands: 1.63 EUR  Belgium: 1.40 EUR  Germany: 1.38 EUR  Italy: 1.65 EUR. There are many websites for comparing gasoline prices across Europe. Prices vary greatly from country to country. Moreover, in Italy, there is a website for comparing the price at different gas stations.
There are many websites where you can compare the price of gasoline in Europe. Prices vary from country to country. Austria is cheaper than Germany for example. Italy has a gas station price comparison website.