| 2007 total production | 2017 total production | |
| Mean | 13,300,000,000 | 13,400,000,000 |
| Variance | 278,000,000,000,000,000 | 379,000,000,000,000,000 |
| Observations | 30 | 30 |
| Pooled Variance | 328000000000000000 | |
| Hypothesized Mean Difference | 0 | |
| df | 58 | |
| t Stat | −1.11975 | |
| P(T<=t) one-tail | 0.133717 | |
| t Critical one-tail | 1.671553 | |
| P(T<=t) two-tail | 0.267435 | |
| t Critical two-tail | 2.001717 |