if you want to use methane as a proxy: http://webbook.nist.gov/cgi/fluid.cgi?Action=Load&ID=C74828&Type=IsoTherm&Digits=5&PLow=.1&PHigh=10&PInc=.1&T=298.15&RefState=DEF&TUnit=K&PUnit=MPa&DUnit=kg%2Fm3&HUnit=kJ%2Fmol&WUnit=m%2Fs&VisUnit=uPa*s&STUnit=N%2Fm or if that link is munged try http://webbook.nist.gov/chemistry/fluid/ also has ethane, propane, butane,.... for methane at 25 C and 1 bar (~1 atm) there are 1542 m^3/tonne