This paper presents the resu[ts of an investigation ofIwo-phase, gas-liquid flow in horizontal pipelines. Experimental data were taken in three field-size, horizontal pipelines, two of which were constructed for this purpose. The data were obtained using water, distillate and crude oi! separately as the liquid phase, and natural gas as~he second phase. Experimental pressure-length traverse, liquid holdup and f?ow-pattern data were collected jor each set of flow rates, These data were used to deve[op three correlations that are presented herein. The liquid-ho[dup values correlated with various flu w parameters without regard to the existing flow pattern. The same was true for the energy-loss factors. A new flow-pattern map is presented that appears to be quire reliable, but not required for the pressure-loss calculations.The liquid-holdup correlation and /he energy-loss factor correlation are used in conjunction with a twe-phase flow power balance, developed during this study, to predict tite pressure bsses that occur during gas-iiquid f70w in horizontal pipelines. A recommended calctdational procedure is given, as weU as a statistical analysis of the results, This procedure lends itself to computer application, since several small pressure decremen [s are needed 10 calculate a pressure-length traverse. The correlations are shown graphically, but may be curve fitted with existing curve-f?tting computer programs,