The stress development in zirconium oxide gel films during annealing between 150 and 400 degrees C has been investigated using thickness and substrate curvature measurements with laser beam reflections. The films' elemental content was determined by Rutherford backscattering spectrometry and their structure by X-ray diffraction. It is shown that the main densification mechanisms are polycondensation reactions up to 300 degrees C with acetylacetone elimination leading to a rather weak stress increase. For temperatures above 300 degrees C the vanishing of acetylacetone favors densification and stress increase.