Provided are methods of filling gaps on a substrate by creating flowable silicon oxide-containing films. The methods involve introducing vapor-phase silicon-containing precursor and oxidant reactants into a reaction chamber containing the substrate under conditions such that a condensed flowable film is formed on the substrate. The flowable film at least partially fills gaps on the substrate. In certain embodiments, the methods involve using a catalyst in the formation of the film. The catalyst may be incorporated into one of the reactants and/or introduced as a separate reactant.