Thank you for your reply. I am still confused because both Oxford and Encarta resources use both on/in behalf of but Longman only uses on behalf of. I have had mixed replies from different sources online and I am not sure which one is really correct.
Hi Anon: I stand corrected, thanks. However, "in behalf of" is rarely used; I don't recall having heard it. The corpus of contemporary American English cites about 2 occurrances of "in" for every 58 of "on" in this phrase.
Thank you for the usage note, AlpheccaStars. That was very helpful. I am more comfortable with "on behalf of" myself but I've been hearing "in behalf of" a lot lately that it got me thinking. Again, thank you.