We performed high-dispersion near-infrared spectroscopic observations of comet C/2010 G2 (Hill) at 2.5 AU from the Sun using NIRSPEC (R ~ 2.5x10^4) at the Keck II telescope on UT 2012 Jan 9 and 10. The comet had been in outburst. Over the two nights of our observations, prominent emission lines of CH4 and C2H6 along with weaker emission lines of H2O, HCN, CH3OH and CO were detected. The gas production rate of CO was comparable to that of H2O. The mixing ratios of CO, HCN, CH4, C2H6, and CH3OH with respect to H2O are higher than those for normal comets by a factor of five or more. Hyper-volatile species such as CO and CH4 were enriched in the coma of comet Hill suggesting that the sublimation of these hyper-volatiles could sustain the outburst of the comet. Based on a comparison with optical observations, some fraction of water in the inner coma existed as icy grains. Those icy ice grains were likely ejected from nucleus by the sublimation of hyper-volatiles.