Mine Safety and Health Administration (MSHA) surveillance data were analyzed to elucidate mine characteristics or injury characteristics that distinguished mines with high rates of transport-related injuries from mines with lower transport injury rates. The results showed that most high-rate mines are small, high-rate mines have a disproportionate number of injuries involving young and less experienced workers, and injuries in high-rate mines are proportionally more severe. Further analyses of the MSHA injury data showed that smaller mines have a greater share of fatal and permanently disabling injuries, whereas larger mines have a greater share of injuries involving no lost time. Based on these results, we explored two explanations for the small mine injury risk: (1) a suggestion that differences in injury reporting between large and small mines may contribute to an apparent small mine injury risk, and (2) identification of factors contributing to a true difference in transport-related injury risk between small and large mines. Whereas it was true that most high injury rate mines were small, most small mines were actually zero-rate, having reported employment but no injuries to MSHA. An analysis employing binomial probability theory showed that a substantial proportion of small mines reported zero injuries when it was statistically probable that injuries would have occurred. This indicated that small mines may underreport injuries relative to larger mines. The possibility that reporting bias affected the associations found in this study was explored by eliminating the least severe injuries from the data set and evaluating changes in associations. This "adjustment" for reporting bias did not change previously observed relationships. Finally, MSHA injury data were analyzed in concert with mining population data collected by the Bureau of Mines. With such denominator information, the results indicated a disproportionately high risk of injury among workers in their first year at a mine and indicated that higher injury risk in small mines might be explained by the fact that workers at small mines have substantially less experience than workers at large mines. An effect of age was not found in these analyses. These results suggest the potential importance of targeted training programs for newly hired miners. Results also point to the need to explore specific factors contributing to the small mine injury risk, and to the necessity for complete and accurate reporting of injury data.