I also saw STP oil at the dollar tree.
After a lot searching I belive this oil was made by Unimark oil it is now know as Cross oil. http://www.crossoil.com/motoroil.htm
I found what I belive is the MSDS on there 5w 30 oil. I could not find one on 20w 50.
I emailed STP and will let you know what if anything I here back from them.