The present invention relates to hydroformylation processes for producing aldehydes. In some embodiments, the process comprises contacting in a reaction zone reactants comprising an olefin, hydrogen and CO in the presence of a rhodium-organophosphite based catalyst, optionally with free organophosphite ligand, and 0.1 to 3 weight percent, based on the total weight of the fluid in the reaction zone, of certain polymers specified herein, such that the solubility of the polymer in the aldehyde is greater than or equal to 1 weight percent at 40° C.