This paper studies sinusoidal and helical buckling of tubulars in inclined wellbores and the ＇＇lockup＇＇ of tubulars due to buckling. The results show that tubular buckling starts from the tubular bottom in low-inclination wellbores, where the axial compressive load is largest due to tubular weight. In high-inclination wellbores it may start from the top portion of the tubular, where the axial compressive load is largest due to frictional drag. This clarifies the confusion on whether or not the tubular buckles at once on its entire length in inclined wellbores. New sinusoidal and helical buckling load equations are presented to better predict tubular buckling in inclined wellbores (0-90 deg). The lower the wellbore inclination angle, the smaller the axial compressive load required to initiate tubular buckling. However, a certain nonzero axial compressive load is still needed to buckle the tubulars in vertical wellbores. When tubulars buckle helically, a large wall contact force will be generated, and the ＇＇slack-off＇＇ weight at the surface will nor be fully transmitted to the tubular bottom due to large resultant frictional drag. The ＇＇lockup＇＇ of tubulars may even occur, where the tubular bottom load cannot be increased by slacking-off weight at the surface.