As Eric mentioned 15 quarts will do ya on 7.3L engines.
I been using Tractor Supply 15w-40 oil and Purolator Oil Filters(identical to Motocraft inside/out) we picked up some four gallons of Walmart 15w-40 Diesel engine oil for the next change based on excellent oil test lab reports from 7.3 owners
Bill
Bill
2002 Excursion XLT-P 4x4 7.3L Powerstroke Diesel