Osmotic effects are important both in static phase behavior and dynamic gel permeation chromatography (GPC) analysis of polymer surfactant systems. Besides affecting the salinity for the II(-)/III phase transition in microemulsions, the water content in the middle phase will decrease when nonassociative, water-soluble polymers are added. The same systems will in a GPC column, using the surfactant solution as eluent, separate both due to osmosis and size exclusion. Association between polyethylene oxide and anionic ethoxylated surfactants disappears if more than three ethylene oxide (EO) groups are added to the surfactant head group. The phase separation of micelles and polymer into separate aqueous, phases in the II(-) state occurred at lower salinity when the number Of EO groups in the surfactant increased. The phase separation could qualitatively be modeled within a simple Flory-Huggins approach. With NMR self-diffusion measurements it was possible to study if added polymer influenced the structure of the surfactant aggregates.