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For UVA corporate account rental through Enterprise click Enterprise Rent-A-Car
There is also Ace Car rental. According to Richard, Ace Car Rental used to allow charges to Fermilab charge codes. Pick up the car near O’Hare. I visited Acre Rentals website (https://www.acerentacar.com/Landing/lp_chic02.aspx) and their prices are not unlike Enterprise. This would be my second choice give the ease of using the UVa contract.
Chicago - Franklin Park
3309 Mannheim Road
Franklin Park, IL 60131 USA
Reservation: 877-822-3872