Com. nonylphenol was ethoxylated with ethylene oxide at 120-180 degrees C on a Ca sulfonate and carboxylate catalyst (content 0.1-0.7% by mass). NaOH was also used as catalyst for comparison. The reaction products contained mainly ethoxylates (ay. ethoxylation degree 8) but also polyglycols (1.0-4.5%), 1,4-dioxane (1.5-4 ppm) and unconverted nonylphenol and ethylene oxide. The ethoxylates produced by using the Ca catalyst showed a narrow mol. mass distribution and contained less by-products than those produced with NaOH catalyst.