McGee at the bottom of page 143 in (http://www-personal.umich.edu/~twod/oil-ns/articles/research-oil/research-oil/john_mcgee_predatory_pricing_standard_oil1958.pdf) mentions Rockefeller’s testimony on forming stable conspiracies. He says Volume 16, 3074-75. However, I have no clue as to how to find this.
On the other hand, this seems of the utmost interest to us here with regard to consipracies in restraint of trade. I suspect Rockefeller was a pretty smart guy and had a thing or two to say about that.