Hydroxyl-containing copolymers of butylene oxide and ethylene oxide having a hydroxyl equivalent weight of at least 150, an average of 1.8 to 6 hydroxyl groups per molecule of which hydroxyl groups at least 70% are primary hydroxyl groups and an oxyethylene content of no greater than 10% by weight based on the weight of the copolymer, are useful for making polyurethanes. These polyols are characterized by high reactivity and fast curing times. Polyurethanes made using these polyols have excellent mechanical properties and are highly hydrophobic.