Pressure drops through oat (Oat Sp.) beds were evaluated in the range of airflow rate from 0·0097 to 0·459 m3/s-m2using two airflow directions to determine the effect of grain moisture and foreign material on the resistance to airflow. Horizontal airflow resistance was lesser than vertical airflow resistance (e.g., for oat with 9·0% moisture content the pressure drop in horizontal direction was 4–17% of corresponding in vertical direction). The resistance decreased with the increase of moisture content and increased when the fraction of foreign material. An increase in the moisture content from 9·0 to 24·9% produced a decrease on the bulk density from 583 to 513 kg/m3. Mattel's model (1969) fitted adequately the experimental data. The Haque et al.'s equation (1982) have an adequate representation of the data for both airflow directions. The Paterson et al. (1971) and Bern-Charity (1975)equations resulted applicable only for vertical airflow direction. A simplification planed of this model in function of the bulk density conduced to a good relation DP-Q.