Carl, I'm not 100% positive but pretty sure from researching in the past that mil and gauge are not the same thing.

EDIT: Ok. I just randomly googled ---- "pool liners mil vs. gauge" and here is one page that came up. I cannot vouch for the accuracy of the info but at any rate, here it is.

http://www.inyopools.com/HowToPage/h..._vs_gauge.aspx