Ok,If oil companies only operate at 90% , because they have to do maintence on the other 10% ,isn't that operating at 100% of thier capacity if the 10% is always of off line.Seems like easy math to me.
If they refine a 900 barrels a day and must keep the maintence going,then to refine 1000 barrels a day,they have to have a capacity to refine 1100 barrels a day in rounded off terms.
In a stretch, theoretically,they could never reach the 100% design capacity ,so in reality theyare producing 100% of what they can.
Again, even considering retrofitting and upgrading, they will not build new refineries that would reduce the price of gas. Retrofitting/upgrading does not significantly increase refinery capacity.
In addition,they might not set the price of oil, but they reap the profit of it's increase.