SBS 0335−052 (upper filled blue circle) and I Zw 18 (lower filled blue circle) on the gas scaling relations given by Daddi et al. (2010). Only Hi mass density is considered for the BCDs studied here; the arrows correspond to the missing gas mass surface density that would transport SBS 0335−052 to the “starburst sequence” and I Zw 18 to the “sequence of disks”. SFR surface density is plotted as a function of the gas (atomic and molecular) surface density for z ~ 0.5 disks (shown as red filled circles and triangles; brown crosses indicate z = 1−2.3 normal galaxies, and empty squares correspond to sub-millimeter galaxies. The shaded regions and filled triangles are local spiral galaxies, and small crosses are starbursts and ultra-luminous galaxies. References for these data are given in Daddi et al. (2010).