http://www.gibsonssteakhouse.com/pdf/Gibsons_Chicago_Dinner.pdf

Gibsons Steakhouse serves steaks graded by the USDA as
“prime”. Currently less than 2% of all beef produced in the
U.S. is graded prime. Our beef programs use cattle that are
proven to be of at least 90% Black Angus heritage. Our
steaks are aged for 35 days and cooked in 1800 degree infrared
broilers. This will give the steak a thin charred crust
which helps to seal in the natural beef juices.