If the group doesn't mind, I'd like to use this thread to document my attempt to reverse engineer a rollover rule-of-thumb for CL.
I realize a rollover rule-of-thumb probably does not exist because:
a) The fine folks here would have already spelled it out

and/or
b) There is perhaps a fundamental difference between CL and ES (in regards to rollovers). Perhaps the supply and demand situation is unique each month and therefore volume relationships are different each month.
With that said, I'll give it go anyway. <g>
So according to my datafeed, this morning on 10/19/2009 the dec 09 contract's volume exceeded the nov 09 volume. I consider today to be the rollover day. So as a starting point for a rollover rule-of-thumb, I'll just count business days back from where the cme/nymex's Last Trading Day rule starts counting from - the 25th calendar day.
The starting CL rollover rule-of-thumb to be tested next month:
"Rollover will be the morning of the 4th business day prior to the 25th calendar day of the month preceding the delivery month. If the 25th calendar day of the month is a non-business day, the rollover will be the morning of the 4th business day prior to the business day preceding the 25th calendar day" (which is what happened this month).
So according to this rule, next month's rollover will be the morning of 11/19/2009. We will see...
thanks,
cT