There is an Open Interest (in CL alone)...not counting QM, or others...
OI for CLQ, CLU, CLV = 534,649 contracts
534,649,000 barrels of oil @ $140 / barrel
= $74,850,860,000
That's just under $75 Billion...
It gets tricker with the CL Options, which have enormous OI..but I'm not sure if...