With xOP on (/msg ChanServ set <channel> xop on) use "/msg ChanServ sop <channel> add <nick>"
Or with xOP off (/msg ChanServ set <channel> xop off) use "/msg ChanServ access <channel> add <nick> 10"
Also there is a lot of information available in "/msg ChanServ help access levels", "/msg ChanServ help access", "/msg ChanServ help vop", "/msg ChanServ help hop", "/msg ChanServ help aop", "/msg ChanServ help sop", "/msg ChanServ help levels" and "/msg ChanServ help levels desc"
[Edited on 18-6-2008 by Jobe1986]