hi RE,
i have always switched over to the next contract the week before expiry. not sure where your getting your vol figs from - this is the cme data for today:
Vol / Change
Sep 12 134,504 0.58
Oct 12 102,002 0.57
IG index change on day is +0.87% vs 0.88%. Still quite correlated, regardless the vol.
The reason behind me changing is partly habitual: the prop firm i used to trade oil at didn't want 1,000 barrels turning up on delivery cos of posNs being left open to expiry - so you had to change the week before; also technical - as they start to diverge in the final week to expiry (not normally til last 2 days though). Its pretty irrelevant to me now as i am trading through an SB.
Light Sweet Crude Oil (WTI)
Please provide the source of the data if you contest.
Thanks.