k_{row}(s_w) \bigg|_{ s_g =s_{gc}} = k_{rcow} \,  \bigg[  \frac{ 1 - s_w - s_{orw}   }{ 1- s_{wi} - s_{orw}  } \bigg]^{n_{ow}}

where

	current water saturation
	current oil saturation,
	initial water saturation
	critical water saturation to oil displacement, below which water is immobile
	residual oil saturation to water displacement, below which oil is immobile
	oil relative permeability curvature to water displacement
	water relative permeability curvature to oil displacement

Initial water saturation maybe equal to critical or less than critical like for example for some petroleogenetic rocks

Fig. 1. Typical Oil-Water relative permeabilities

See also