All of our existing refineries have made major upgrades and taken steps to increase output. This is why there was a sudden “unexplained” spike in prices last summer. We were at about 75% of our production capability because several major refineries shut down for repairs and modification. Two were retooled to meet Federal mandates for blended fuels.
The biggest reason there have been no new refineries built, is the extreme cost to build them in this day and age. The Oil companies operate at such a small profit margin, (8-10%) there simply is not enough money for them to do it and also meet their exploration goals. (Both of which are paid for by profits.)