the EPS showed increments during the same period. The biggest increase in number can be seen in Exxon's net assets per share over the eleven years: the net asset per share inflated over six times its original figure, from $8.15 to $51.39. Subsequently, there was a large increase in the EPS as well as in the number of stocks outstanding. SoCal also saw a huge jump, more than doubling its initial net assets per share.
Thus, we find that the levels of concentration in the U.S. petroleum industry, although quite high compared to other industries, have gone down to some extent in recent years. The concentration ratios were much higher in the petroleum refining sector than in crude production, the former showing the least change during the last twenty-five years. But the relative degree of concentration was extremely high in this industry, as was seen in the Gini Coefficients and the Herfindahl Indexes. However, there were a tremendous number of entries and exits in the crude production sector while entries in petroleum refining were virtually nonexistent in later years.
Measuring the economic and financial performances, the growth rate of assets in this industry was spectacular throughout the period, but it was negative when the growth rate of number of new firms was taken into consideration in both sectors. Regarding net profit margins, 1973 was the best year for the industry from among the selected years mainly due to the rise in inventory profits following OPEC's price boosts of crude oil. But the profits decreased considerably in 1979, making them similar to other industries in the manufacturing sector. It is doubtful that the U.S. petroleum industry will undergo another period of lofty profits such as it witnessed in the recent past.