Hope this helps:
'OSCCON VALUES FOR 16F818/819:
'OSCCON = $00 '31.25 khz DEFAULT
'OSCCON = $10 '125khz
'OSCCON = $20 '250khz
'OSCCON = $30 '500khz
'OSCCON = $40 '1mhz
'OSCCON = $50 '2mhz
'OSCCON = $60 '4mhz
'OSCCON = $70 '8mhz