A family of hydrocarbon liquids has been discovered that is stable at temperatures up to about 400 degrees C in the presence of synthesis gas. The performance of a commercial, ’zinc chromite’, ’high pressure’ methanol synthesis catalyst was evaluated in a slurry reactor using two of these liquids, decahydronaphthalene and tetrahydronaphthalene, to suspend the catalyst. The evaluation covered a range of temperatures from 275 degrees to 425 degrees C, total pressures from 6.9 to 17.2 MPa, H-2/CO ratios from 0.5 to 2.0 and space velocities from 1500 to 10 000 sl kg(catalyst)(-1) h(-1). Methanol was the only significant product at the lower end of this temperature range. The methanol synthesis reaction was close to equilibrium at the highest temperature, and there were significant quantities of dimethyl ether, olefins, methane and carbon dioxide in the product. Catalyst performance was sensitive to the composition of the slurry liquid, but was relatively stable in decahydronaphthalene over a long period of time.