Improving the energy efficiency of residential and office buildings is an important way of reducing energy consumption and CO2 emissions and eliminating their associated adverse environmental impacts. On the other hand, people spend the majority of their times in buildings and demand comfortable, healthy, and productive indoor environments. Building energy conservation and occupant comfort are usually considered to be conflicting objectives. Towards exploring ways of reducing building energy consumption without sacrifice in thermal comfort, this paper aims to study the relationship between energy use mode, thermal comfort, and energy consumption in office buildings. To conduct an initial experimental study, a floor of an office building in Philadelphia, PA, was instrumented and monitored. Cooling energy consumption, indoor temperature, occupant feedback on thermal comfort, and outdoor temperature data were collected for three months. A clustering algorithm was used to identify three energy use modes: saver, balanced, and spender. The correlation between building operation efficiency and thermal comfort was investigated, and thermal comfort levels under different energy use modes were compared. The results show that there is a very weak correlation between building operation efficiency and thermal comfort, and that there is not a significant difference in thermal comfort across the three energy use modes. The findings of this study may help in identifying building operation strategies that reduce energy consumption while remaining thermally comfortable.