What I think I am seeing here is crude inventories declining as prices rose from $10 to $30 per barrel, then slowly rising as price rose to $50 per barrel. After that we see strong inventory build even as prices climbed to nearly $80 per barrel, then declining inventories as prices rose towards $100 per barrel.

What does this suggest to me? My first impression says to me that the oil companies did not believe that $30 per barrel was justified and chose not to buy, but as prices failed to retreat they began to slowly accept this. Then as prices rose higher they realized that yes, oil supplies really were becoming seriously constrained (we can argue about peak later but definitely constrained). The oil refining companies seem to believe that oil was reasonably prices all the way to about $80 per barrel. As prices rose above that though, their buying falls back and indicates that they do not believe it is worth that much. Whether these beliefs are justified or not is a separate matter. I make this analysis because even though the graph does not show this, we know that the price increases have been very steady since 1998 in a generally rising trend.