If you plan on having the car forever, change it every 3,000-3,500 miles or every 3-4 months. Everyone is a little different, and many change theirs at 5,000 miles. I, along with most everyon on this forum, agree that 3,000 miles is a good distance to go between oil changes.

But if you do a search, you will find a ton of info. Oil is a hot topic around here!! Good luck.

__________________
2006 E350 w/ 155k miles (Daily Driver)

Previous:
1993 300E 3.2L Sedan w/ close to about 300k miles
2003 E500 Brilliant Silver (Had 217k miles when totalled!)
1989 300E with 289,000 miles (had for <1 yr while in HI)
03 CLK 500 cabrio (Mom's)
2006 C230k (Dad's)
1999 S420 (Mom's/Dad's)
2000 C230k Sport sedans
2001 CLK320 Cabrio (Mom's)
1995 C280 My First Mercedes-Benz... (155k miles. EXCEPTIONAL AUTOMOBILE. Was Very hard to let go of!)