XD30 and XD50 are oils sold by BRP for Evinrude and Johnson two stroke motors.
XD50 has a built-in carbon treatment so you don't need to pay extra for a carbon preventative additive if you use the XD50.
TC-W3 is a national rating for oils that are for
Two
Cycle-
Water Cooled outboard engines:
http://www.nmma.org/certification/programs/oils/
http://www.nmma.org/certification/local/downloads/documents/TC-W3-2009.xlsx
TC-W3 is a minimum standard; most long term users prefer synthetic or synthetic blend TC-W3 oils.