An aldehyde composition derived by hydroformylation of a transesterified seed oil and containing a mixture of formyl-substituted fatty acids or fatty acid esters having the following composition by weight: greater than about 10 to less than about 95 percent monoformyl, greater than about 1 to less than about 65 percent diformyl, and greater than about 0.1 to less than about 10 percent triformyl-substituted fatty acids or fatty acid esters, and having a diformyl to triformyl weight ratio of greater than about 5/1; preferably, greater than about 3 to less than about 20 percent saturates; and preferably, greater than about 1 to less than about 20 percent unsaturates. An alcohol composition derived by hydrogenation of the aforementioned aldehyde composition, containing a mixture of hydroxymethyl-substituted fatty acids or fatty acid esters having the following composition by weight: greater than about 10 to less than about 95 percent monoalcohol {mono(hydroxymethyl)}, greater than about 1 to less than about 65 percent diol {di(hydroxymethyl)}, greater than about 0.1 to less than about 10 percent triol, tri(hydroxymethyl)-substituted fatty acids or fatty acid esters; preferably greater than about 3 to less than about 35 percent saturates; and preferably, less than about 10 percent unsaturates. The alcohol composition can be converted into an oligomeric polyol for use in the manufacture of polyurethane slab stock flexible foam.