1 INTRODUCTION
2 OBSERVATIONS AND DATA REDUCTION
2.1 The COSMOS-[OII] Survey
2.2 COSMOS-[OII] Observations
2.3 Data Reduction
2.4 Emission Line Fitting
3 SAMPLE SELECTION
3.1 The $z\sim1.5$ Sample
3.2 Local Comparison Samples
4 ELECTRON DENSITIES
4.1 Methods
4.2 Electron Density Samples
4.3 Electron Densities at $z\sim0$ and $z\sim1.5$
4.4 Electron Density vs. Redshift
4.5 Electron Density vs Global Galaxy Properties
5 SUMMARY