Correlation plots for the outflow force F_CO using M1, bolometric luminosity L_bol and the mass of the envelope M_env. Black diamonds are from this study, red triangles from CB92, and blue circles from Hogerheijde et al. (1998), where F_CO was calculated by the same method as in this study. The Class 0 sources are encircled. Upper limits are indicated with arrows. The dashed line indicates the best fits to the combined data set.