oci_connect returns warning if provided with the 4th param(charset)

Hi all, I used the following in my code .... oci_connect('$user','$pass',$connectionString,'UTF8'); .... and got the following warning: Warning: oci_connect() [function.oci-connect]: Invalid character set name: UTF8 I tried many times and found it could only work when I removed 'UTF8' or replaced it with 'US7ASCII'. It didn't work even I used 'WE8ISO8859P1'. But I had to use 'UTF8' in order to support multiple bytes. I had tried setting NLS_LANG to AMERICAN_AMERICA.UTF8 in envvars instead of using the 4th parameter in oci_connect, but it didn't work. Using putenv to set NLS_LANG didn't work either. Does anyone encounter this weird issue before? The php version I'm using is 5.2.1. Thanks for any help.