N,N'-(4-Methyl-1,3-phenylene)bis(N-(1,5-dimethylhexyl)ureal or DMHUT, a low molecular weight bisurea with branched alkyl substituents, is capable of thickening high-pressure propane, which could lead to improvements in its performance during miscible enhanced oil recovery and waterless hydraulic fracturing. DMHUT dissolves in supercritical propane upon heating to 115 degrees C at high pressure (34.5 MPa). Upon cooling to temperatures as low as 25 degrees C the solution remains a transparent, stable, single phase that exhibits remarkably high viscosity. For example, at a mass fraction of 0.5 wt% at 40 degrees C and 34.5 MPa, falling ball viscometry indicates that the bisurea-propane solution is more than 400 times as viscous than pure propane. The thickening efficiency of DMHUT has been found to be superior under most conditions to other small associative molecules and polymers known to thicken propane: tributyltin fluoride, hydroxyaluminum di(2-ethylhexanoate), ultra-high molecular weight poly alpha-olefin, or conventional crosslinked phosphate esters based on long-chain alkyl-substituted phosphate esters.