The "Late Era Big Four" refers to the oil fields producing the most up until peak oil, and for some years afterwards. The peaking of these four fields at roughly the same time created a perfect storm, which reduced world oil "production" substantially over the next few years. All of these fields used advanced technology (horizontal drilling, water pumping, etc) to get out oil at super-fast rates up until their peaking, but this led to their ultra-fast decline rates, too.