Each time you enter sqlplus ORACLE looks for a file in your current directory called login.sql. In this file you can place any SQL*Plus command that you wish to be globally applied to your work. Thus to save typing in common format or page commands at each session they can all be placed in a file called 'login.sql'. So you can add the param set autocommit on. A typical file might be:

SET PAGESIZE 22
SET PAUSE ON
SET PAUSE "Press <ENTER> for next page"
SET PAUSE "Press <E>
SET NUMF 999999
COL ENAME FORMAT A15
COL SAL FORMAT 99,999.99

If you enter sqlplus from a directory level other than that in which the file login.sql has been placed, ORACLE will not find it and the settings will not be applied.
P.s autocommit is not recomanded.