Crew oxygen is gaseous - a fixed bottle to fixed masks in the flt deck and portable bottles for crew so they can go about their duties in the cabin. Pax oxygen is invariably by oxygen generators and those basic unsealed masks on airliners as pressurised gaseous oxygen would be far to heavy and maintenance intensive. I suspect it'd also be too dangerous - a leak from a single portable oxy bottle can be dealt with simply by removing it from the vicinity of any fire, but a leak in a system that caters for the entire aircraft would not have that flexibility, and would also render oxygen unavailable for the entire passenger compliment rather than just a seat row, as would happen for an oxygen generator failure.