Liquid slug flow in oil production well flowlines and the like is controlled by a throttling valve in the flowline upstream of a gas-liquid separator and a differential pressure gauge, densitometer or other device for measuring the presence and the volume of the slug in the flowline. The throttling valve may be actuated to throttle fluid flow into the separator in relation to the presence of the slug and the duration of the slug as determined by the slug detection device. Slug mitigation may also be controlled by throttling flow into the separator in relation to the level of liquid in the separator between a threshold level and a maximum liquid level. A third method for mitigating slug flow measures the available volume in the separator vessel and the volume of the liquid slug moving toward the separator vessel to effect proportional throttling of fluid flow. A liquid slug may be detected by a differential pressure gauge or a densitometer interposed in the flowline upstream of the throttling valve.