Ratio of oil production rate q_O to water injection rate q_{WI}:
| (1) | {\rm PIR} = \frac{q_O}{q_{WI}} |
It measures how efficiently the injection supports the oil production.
The PIR can be expressed through the current VRR as:
| (2) | PIR=\frac{q_O}{q_{WI}} = \frac{1}{VRR} \cdot \frac{1-Y_w}{Y_w + (1-Y_w) \, \left[ \frac{B_o}{B_w} + \frac{B_g}{B_w} \, ( GOR - R_s) \right] } |