Texas peaked at 54% of Qt.  Average net decline rate, after new wells, workovers, secondary/tertirary recovery:  4.1% per year.

Saudi Arabia is at 55% of Qt.

These were the two principal swing producers, and each one served as a swing producer for about 35 years.  Texas, 1935 to 1970, and Saudi Arabia, 1970 to 2005.  

I think that a useful plot would be 21 years of Texas production data, 10 years on either side of 1972, with 11 years of production data for Saudi Arabia also shown, lining Texas in 1972 up with Saudi Arabia in 2005, with different vertical scales.  Since we only have crude + condensate for Texas, I would use crude + condensate for Saudi Arabia.

Imagine, if you will, what a Texas oilman--then proud of Texas' record high oil production--would have said in 1972 if you told him that oil prices beyond the dreams of avarice were just around the corner--a 1,000% increase in oil prices over an eight year period, that Texas would respond with the biggest drilling boom in history, that we would increase the number of producing oil wells by 14%--and oil production would drop by about 30% from 1972 to 1982.