I believe that one major way to fill the SPR in the past was to exercise a clause in every mineral rights contract that involved federal lands which basically gave the SPR first rights to a specific percentage of each such well's production. Thus if production from those wells holds steady for 6 more months (a fairly reasonable short term assumption) then they can project that amount coming in. I think of it as a direct tax on the production of oil from federal lands. It doesn't "cost" the government anything but it is production "lost" to the producer as a concession to government.

This may be how they know what to expect incoming.

I think an exchange is where you swap seet for sour etc.

Coul be wrong.