Do you realize how little 2 million barrels is? It fits on one  VLCC super-tanker. That might be a clue as to where it is "floating" around. There are plenty of tankers in the world - more than enough to hold an extra 60 million barrels, or even 120.
Nice point about the supertankers. Now, the supertankers in the aggregate serve as the pumps of a pipeline. If they slow down to save diesel, that'll slow delivery but the in-transit crude remains the same - just like slowing pipeline pumps.

However, just like a pipeline, that crude-in-transit isn't like a SPR where you can vary the "reserve" from zero to full. Becuse these ships are slow in the first place, there is no JIT delivery. The ships have a top speed of like 15 knots (17mph) so a trip across the Atlantic is no crosstown drive.