High-temperature in-situ H-1 NMR with a probe operating at a frequency of 100 MHz has been used to quantify the effects of particle size, mild oxidation, and different heating regimes on plasticity development for a low-volatile Australian bituminous coal in terms of the proportions of rigid and fluid material present. At the temperature of maximum fluidity, the fluid phase accounts for 35% of the hydrogen remaining, with both its concentration and mobility increasing up to this temperature. Reducing the particle size below ca. 150 mu m suppresses plasticity through a reduction in the mobility of the fluid phase with the concentration of rigid material remaining constant. This effect is considerably more pronounced with slow heating than it is with fast heating (3-4 cf. 30 degrees C min(-1)). In contrast, suppressing the fluidity by mild oxidation reduces primarily the concentration of the fluid phase. Isothermal treatments give rise to a loss of fluidity due to reductions in both the proportion and mobility of the fluid component. The in-situ measurements have confirmed that plasticity development is a reversible phenomenon provided that relatively fast quenching rates (ca. 75 degrees C min(-1)) are used. These results are discussed in relation to estimating the contribution to fluidity development from the non-solvent-extractable material in coals. Heating coking coal in a tube furnace to the temperature of maximum fluidity followed by fairly rapid cooling is shown to be a simple procedure for recovering relatively large amounts of partially carbonized coal with the structural features responsible for maximum fluidity preserved.