What is the make and model of spark plug?
How long were they installed?
Are they the proper heat range (Bosch "9")?
What is your measured rate of oil consumption?
How about driving habits. Do you do a lot of short trips - say less than five miles?
What do you mean by fouled? Tan colored oil ash deposit buildup on the insulators is normal if the engine has fairly high oil consumption, but may be due to too cold a plug. Dry black carbon deposits could be an indication of a rich mixture or too cold a plug. Wet black deposit buildup could be an indication of oil consumption or too cold a plug.
Any of these indications could also be a result of short trip driving.