I suspect most do. But some of those, particularly smaller refineries, may be producing one product that does not yet meet ULSD and have a much more limited market. Eventually they will have to change.
costs are the same...
Everything correct until that. Cost are not the same. Essentially every refinery has to add new or enlarged hydrotreat desulfurization units, or buy much higher priced very sweet crude oil. Even after built running fluid through those units is $/barrel.
Also, some of the larger refineries are essentially 2 or 3 refineries inside one fence. Some have complete trains for all the processes with even separate storage yards. They share some utilities and have the ability to move product from one to another, but normally don't.
Those must be the older plants.
When the switch was made at Pine Bend, it took about 15 seconds to decide to make 100 percent low sulfur.