Blackstone labortories summerises it very well .
"You can go into any mass retailer (Wal-Mart, Meijer, AutoZone, etc.) and buy a 5W/30 (or any other grade) that will perform well in your engine. One of the best-kept secrets of the oil industry is that these store brands are actually the same, quality oils that are produced by the major oil companies. The only difference between these products and the major company brands is the name on the container and the price. Don’t believe us? Try running your own experiment: do a sample on Oil A after a known number of miles, then do a sample on Oil B and compare the wear levels. You may see a little fluctuation, but it’s very rare for one oil to make a significant difference in an engine’s wear patterns."