The performances of kriging, co-kriging, and kriging combined with regression were compared. These last two methods were applied to improve the interpolation of the soft-layer depth (Dsl), using the bulk soil electrical conductivity as an auxiliary variable. Soft layers were not detected within the boring depth of 1.20 m at 10% of the locations. Special attention was paid to these so-called censored observations on Dsl in the regression analysis and in the interpolations. Kriging combined with regression gave better results than co-kriging. Moreover, in kriging combined with regression fewer model parameters needed to be estimated.