Anyone use Sierra oil? My local pats store stopped handling Merc oil.

There are a lot of suitable oils. I would think a lot of those are better that Sierra.

I had to make a run to Petoskey, I picked up some merc oil, problem solved.

Its all made in the same place, branded different. base stock is the same, sometimes they may alter the ratios of the additive package. If it has the right stamp recommended 'BIA' TCW3 NMMA etc it must be good.
Mercury, walmart, Sierra, BRP don't have there own refinery. There are only 3 refinery companies in north America. Everyone else orders what they want and uses there own marketing machine of BS to sell it.
If it is labeled with the ratings and certifications you need, its fine.

Citgo makes / blends a lot of oil for the marine OEM's. 2 stroke and 4 cycle oils.

Citgo also makes gear oils for some of the marine OEM's. Mercruiser gear oil is made by Citgo but Mercruiser high performance gear oil (green color) is made by Bel Ray.

Also I think there is only 6 or 7 additive companies left that the oil blenders can buy from. Shell, Mobil & Lubrizol are 3 of them.

I think the Sierra motor oil falls under a group II for their base stock. There is a difference in oil brands especially on the base stocks side of things plus the additive packages being blended into the base stocks. Group I thru III and Group IV & V in which are your true synthetic oils for base stocks.

While this is true as far as refineries go, there are hundreds of "blending" plants that mix in the propriety additive packages to meet specifications. Personally I would stick to an off road oil of some kind. EPA regulations and new car technology is forcing oil manufactures to remove some of the additives that are beneficial to our older technology and high strain environment.

That being said....when is the last time you heard a machinist say "Yup, she blew up because you brand x oil, if you used brand y this would not have happened" ? Personally for me....never

Mercury/Sierra 25W - 40 oil is a 25 straight weight and a 40 straight weight oils combined together. Same oil. Same drive oil also.

I have no idea where you came up with only 3 refining companies. I can assure you that I work for many more than that.

In no particular order.

Exxonmobil

Shell Motiva

Total

BP

Phillips

Citgo

Koch

Chevron

Houston Refining

Valero

Sunoco

Marathon

Hovensa

Lubrizol is behind many of the after marker oils