A new model describing transport across lipid membrane was developed based on the Statistical Rate Theory (SRT) of interfacial transfer. In our calculations we replaced lipid membrane with well-defined octanol membrane. According to SRT the rate of solute transfer across water/octanol interface depends on the ratio of solute concentration in the both phases and the water/octanol partition coefficient. In the case of thick membranes and thick diffuse layers our model predicts almost linear dependence of flux on concentration gradient. However, for thin membranes and thin diffuse layers flux becomes nonlinear function of concentration gradient, especially for more polar solutes and higher gradients.