A private car rental is not ideal in Upper Egypt. It's easier and usually no more expensive to have someone drive you.
If you want to tour the Nile Valley on your own schedule, the best options are to hire a private car and driver—usually called limousine service—or take a taxi. Several of the better hotels publish set rates for popular destinations, and the taxis they work with will agree to the rate schedule. The limousine companies offer rates that are very competitive with, and sometimes even lower than, what you can haggle from a taxi driver; you’ll be going in a nicer vehicle; and the company can help obtain the required police permission if you’re going to sights farther afield. Traveling by car in Egypt is not the freewheeling experience found in Western countries. For security reasons, foreigners must obtain police permission, at least 24 hours in advance, if traveling by auto beyond the city’s immediate tourist spots, and there are checkpoints along every route, with certain destinations requiring police escort.
El Sahaby Limousine Car. Shar'a Luxor-Karnak, Luxor, Luxor. 095/235–7980; 010/522–6582).
Far & Beyond Travel. 1 Shar'a Salah el-Din, Luxor, Luxor. 095/228–7990; 010/888–7666.