A slug mitigation system for subsea pipelines includes a riser located between a low level and an upper (above sea-) level of a pipeline, where an inline separator, e.g. an “I-SEP”, is located upstream of a first stage separator. A throttling valve or fixed restriction is located downstream or upstream in series with the inline separator. Further aspects may also include a surface jet pump upstream of the in-line separator and/or a cyclonic separator downstream of the in-line separator.