In vehicle oil, brands like Napa oil is the same thing as Valvoline, same oil just packaged in another bottle and a cheaper price.  Is the same for outboard oil.  Are the other brands the same oil as the mercury/yamaha/johnson name brand oils.  If so which is the best buy?  Thanks for the help.

Great question, difficult answer.

There are just so many refrineries in the USA and their finished products are sold under a number of lables.

In addtion, some retailers will have changes in the formula incorporated into their products to make the processing less expensive.

I try to look at the ingredients in different products to compare them with the ingredients in the major brands.  For example, asprin is asprin.  10W30 should be 10W30 motor oil. 87 octane gasoline is 87 octane gasoline.  However, the higher quality brands usually add another additive to the product to try to make it better.

All I can suggest is that you look at the ingredients to compare and then make up your mind.

Of course, when it comes to my boat I always use the top of the line products as I don't want to be stranded in open water just to save some pennies.

As mentioned, not but so many refineries, and they may make 10 different brands, might make the Johnson/Evinrude and might make Pyroil but don't think for a minute they are all the same.  Keep your motor happy, buy a quality, name brand.  

Another question about outboard oil.  Im new to all this with the motors and all, I just recently purchased my first boat.  Anyway I have an Evinrude 130 on it and i was looking on line at oil and was wondering what would be suitable to run in that motor.  I was looking at Johnson/Evinrude oil and they were like the X25, X30 and X50.  Im sure the numbers are for different weight oils, but which weight would be a good to run?

I use Yamalube oil.It's a brand new outboard and the dealers suggested to stick with the oil that Yamaha has for its outboards.I know they're saying this to get me to buy their oil,but why take any chances?Works great and with the mixture at 100:1,It takes me a couple of months to go through one bottle of it.