Three Ryco oil filters (from three different cars)
Top; after 20,000km (12,000 miles) in a conventional set up. Nothing unusual here.
Middle; after 40,000km (24,000 miles) in a car on gas (LPG) and with a bypass oil filter. I normally changed the OEM oil filter and oil at 50,000km intervals. There's stuff all carbon when you're running on gas. I'm sure you don't have to change the oil or filter this often, with this set up, and the oil never looked black on the dip stick, just stayed yellow.
Bottom; from a Ford Falcon on LPG after about 10 years and 300,000km (180,000 miles) This one changed my opinion of Ryco filters from good, to bloody good.