hello, my brain is mush this mornin, and ive forgotten everything i know about sorting, so maybe you guys can help

i have an array of things, lets say x, each x has an O2 and a thickness. I want to sort the x's in order of their O2 and.......... uh nevermind the rest, hehe. i'll get onto that later.

the array of x can vary in length from 1 to 20, yes, that's right it must sort a max of 20

and ideas?
thanks for your time
Ang