Bubble formation from a single nozzle is investigated analytically and experimentally in nonaqueous Liquid and liquid-solid suspensions at pressures up to 17.3 MPa. A mechanistic model is proposed to predict the initial bubble size in liquid-solid suspensions, by taking into account the various forces affecting the bubble growth including those induced by the presence of the particles, such as the suspension inertial force and the particle-bubble collision force. It is found that the initial bubble size in the suspensions is generally larger than that in the liquid mainly due to the inertia effect of the suspension. The initial bubble size increases with the solids holdup. The pressure has an insignificant effect on the initial bubble size in both the liquid and liquid-solid suspensions under the conditions of this study. The model can reasonably predict the initial bubble sizes obtained in this study and those reported in the literature.