I live in Salt Lake City and drive about 100 miles round trip per day, most interstate, and go over a mountain pass with pretty good changes in grade twice per day. I go through a lot of oil changes, and euro formulated oils are sometime hard to find, and rarely on sale. Costco has M1 on sale right now, but my local Costco does not stock the Euro formulation M1. I drive a 2005 S500 with 175k miles, also have a 2006 s500 4matic with 5ok miles, I only drive the 4matic in really snowy conditions as it's fuel mileage is about 25 percent less than the rwd version (likely because the RWD has seven speed trans, the 4matic only 5 speed).

I was able to purchase a qty of Pentosin Euro 5w30 for $2 a quart. I have been doing a lot of reading, and it suggest 5w30 is ok for city driving, but high speed over mountain passes- the 0w40 or 5w40 should be used.

Any thought son using the 5w30 instead of the 5w40 in my S500 specked for 5w40?

You're fine. It has the following approval: Mercedes-Benz 229.5

It's a "heavy" 30w.

Your “high speed driving” isn’t the same as the high speed driving in Germany. 130mph+ for a couple of hours on the autobahn and you may need the 40wt. Use the 5w30.

As has already been noted, grade is virtually irrelevant with the Mercedes Benz approval (mostly a choice of winter rating.) It would be nice if Pentosin listed the approval properly on their sheet but it does appear on the BeVo website.

ONLY thing that matters is MB229.3 and even better MB229.5.
Anything 0W30, 5W30, 0W40 or 5W40 with those approvals, preferably MB229.5, is OK, mountain driving or not.

Any oil meeting MB229.3 for gas Mercedes befor 2009 or MB229.5 for MB after 2009 is more than fine regardless of grade in Germany too.

Thanks Gents- grateful for your comments. Went around and picked up another 30 quarts today. At $2 a quart, might be a good buy for some. Just realized my post did not mention the Retailer- AutoZone...

I will make a run tomorrow. I could use it in wife's Tiguan or for a 335i or A4 I plan to get next year.

Now there's a sign of a true BITOG'er! Buying oil for a car he doesn't own yet lol.

A4's are awesome, my favorite when I shopped last year but in the end new VW with killer warranty trumped cool comfy used A4. May get one next time around anyway. The 3 series also tugs at me but I have no experience with BMW and am inherently suspicious of them. Long history with VW and Audi.

I am aiming at E90 2011 335i with stick, of course, and sport package. However, they are sooooooooo hard to find with decent mileage. Next option is 328i (they all have to be xDrive as I drive a lot in mountains in winter) also stick, sport package 2009-20011. If I do not find decent, I will look at A4 2.0T S-line. I tried several and they move, and handling really good. Interior is notch in higher quality over BMW E90, but while not an issue as car is well planted, there is less neutrality and always present understeer compare to BMW. Of course, steering in E90 is just unmatched by any.
Now, I might be able to swing 2013 S4 maybe. Not sure whether I will go F30 3 series as except being very neutral, and having inline 6 in 335i, is very soft. I actually think A4 has better steering than F30 3 series.
Now, once I get one of these, I can park my Toyota and drive it ONLY in case i cannot fit 7 people in BMW or Audi.