What type of forces are being overome when liquid oxygen boils at 90K?

When liquid oxygen boils at 90K, the primary forces being overcome are intermolecular forces, specifically van der Waals forces. These forces hold the liquid molecules close together, and as the temperature increases, the thermal energy becomes sufficient to overcome these attractive forces, allowing the liquid to transition into the gaseous state. This phase change occurs as the molecules gain enough energy to escape into the vapor phase.