The relationship between the gas-liquid two phase flow and the formation of dead space in the throat of a horizontal ejector with liquid jet was investigated experimentally. The flow modes in the throal can be classified approximately into three regimes which present a different kind of bubble formation and gas-liquid mixing. The relationship between the values of pressure in a chamber of the ejector, P-s, and the principal operating factors was investigated in the case of single and multi nozzles. As a result, an empirical correlation by which the observed values of P-s can be predicted within an error of +/-5% was obtained. The relationship between the start points of bubble formation in the throat, L(c), and the operating conditions was also investigated. As a result, two empirical correlations by which the observed values of L(c) can be predicted within an error of +/-25% were obtained for single and multi nozzles. Moreover, experimental data were investigated from the view point of the relationship between flow pattern and longitudinal distribution of the static pressure. As a result, a characteristic curve by which the observed flow patterns can be predicted was obtained.