Qatar is filled with RENT A CAR shops and I'm really surprised that you have posted a thread about it.
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Anyhow, you can find alot of rent a car shops on MATAAR QADEEM [OLD AIRPORT ROAD]
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Moreover, go to QTEL online directory and u will get the list of all RENT A CAR shops.
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CLICK THE LINK BELOW:
http://www.qtel.com.qa/ImpSearch.do?catList=9&subList=5