R/P ratios represent the length of time that remaining reserves would last if production were to continue at the previous year’s rate.

It is calculated by dividing remaining reserves at the end of the year by the production in that year. The world’s oil R/P ratio in 2006 was 40.5 years compared to 41 years in 1996 and 39.8 years in 1986. The world’s natural gas R/P ratio was 63.3 years in 2006