  We show that phase separation can occur in a one-component liquid outside its
coexistence curve (CX) with addition of a small amount of a solute. The solute
concentration at the transition decreases with increasing the difference of the
solvation chemical potential between liquid and gas. As a typical
bubble-forming solute, we consider ${\rm O}_2$ in ambient liquid water, which
exhibits mild hydrophobicity and its critical temperature is lower than that of
water. Such a solute can be expelled from the liquid to form gaseous domains
while the surrounding liquid pressure is higher than the saturated vapor
pressure $p_{cx}$. This solute-induced bubble formation is a first-order
transition in bulk and on a partially dried wall, while a gas film grows
continuously on a completely dried wall. We set up a bubble free energy $\Delta
G$ for bulk and surface bubbles with a small volume fraction $\phi$. It becomes
a function of the bubble radius $R$ under the Laplace pressure balance. Then,
for sufficiently large solute densities above a threshold, $\Delta G$ exhibits
a local maximum at a critical radius and a minimum at an equilibrium radius. We
also examine solute-induced nucleation taking place outside CX, where bubbles
larger than the critical radius grow until attainment of equilibrium.
