Would like to get a sense of what the price of gas/petrol is in Germany. Need to know for figuring out full cost to rent a car .
Thanks for your help.

Go google it, there are websites about this.

I would guess 1.35E or so a liter.

http://www.clever-tanken.de

about
Diesel 1.19€
Super Unleaded 1.40€
in Munich

If you enter town names or zip codes, the site will show the current prices and cheapest gas stations in the area.

about
Diesel 1.05€
Super Unleaded 1.15€
in Salzburg

We just returned from Germany last week, prices vary from 1.35 -1.47 Euros per liter, diesel cheaper. Austria was far less .99 - 1.23 liter.

Switzerland is cheaper for gas/petrol too (1.16 euro, priced in Swiss Francs), diesel about the same.
France a little cheaper for petrol (1.32 euro), about the same for diesel.
Prices vary from station to station in Germany, so it pays to shop around. Usually cheaper where there's a lot of competition, most expensive on Autobahn (as in most countries).

And Sanmaun / Switzerland has the following prices today.

Diesel 0.877€
Regular 95 0.926€
Super 98 0.968€

http://www.eurocenter.ch/

Samnaun!

I had no idea swiss gas prices were so much less than spain.

They don't all take credit cards either, so its cash only for visitors. (The locals have a strange German card but you have to have a German bank account to get one)

In Samnaun, they take any credit card. A local told me that when the tax inspector first came a few centuries ago, they just sent him back. . Since then they don't pay taxes. The village is owned by two families one of them owns all the gas stations. They sell watches and booze too. It's not really far from Munich so fill up you car. And get some booze, watches or whatever.

Cheap stuff... NO TAXES!

'I had no idea swiss gas prices were so much less than spain.'

The prices quoted above by logos999 for Samnaun are special duty-free rates only available in Samnaun, a duty-free enclave within the canton of Graubünden. Regular Swiss prices are much higher, as I've quoted.

As for Germany, credit cards are usually accepted, esp those service stations belonging to big oil companies like Esso, Shell, Aral, Mobil and RWE. Some independent stations only take EC-Karte, which should be affiliated to Maestro debit cards.

Yes, Samnaun is the place to go, if you need gas/petrol or booze

Seems worth a short detour if you are in the area!

Alec is spot on re. the cards.
The cheapest stations are usually independents and/or located at shopping centers and you rarely can use CC but only DC there. But using your US debit card might incur transaction costs that can easily exceed the one or two cents per liter you save there.
The regular chains all accept CC.

For calculating the full costs of a rental you obviously need to know the car's consumption. Most modern European compacts or intermediates don't need more than 6 or 7 liters/100kms, or less if you can avoid city traffic, and when you heed your speed on the motorways.

So if you plan to drive 1,000kms, and get a regular rental car you may pay around € 100 for gas in total, or appr. € 85 if it's a diesel. (calculated on 7 liters/100kms and €1.40/l gas or €1.20/l diesel)
If you find gas stations which are 5 cents cheaper, you overall savings, calculated for the whole 1,000kms road trip, would be around € 5 for either fuel in total.
Not that much money IMO.