This study estimates the demand for domestic air travel services in the United States in order to calculate the fare and expenditure elasticities of demand. We segmented the market according to number of operating airlines, distances and traveler types. Using Seemingly Unrelated Regression to estimate the Almost Ideal Demand System (AIDS), we find that the expenditure and uncompensated own-fare elasticities are around unity and consistent with the previous literature. Results reveal a tendency of uncompensated own-fare elasticity to decrease as distance increases, and a tendency of uncompensated own-fare elasticity to increase as number of airlines increases. Due to few observations, business travelers' results are not reliable to make any conclusion. Leisure travelers' results are closer to all travelers' results.